Plant physiology and ecology

Preface

The point of view and the methods of study first advanced in " Research Methods in Ecology" have proved so satisfactory in teaching as to make it desirable to embody them in a text-book. The present text has been based largely upon " Research Methods," though most of the matter is new or rewritten. The manner of treatment is essentially the same, but the subject-matter has been rearranged and broken up into a larger number of chapters. The plant is first considered as an individual, with respect to factor, function, and form, and then as a member of a plant group or formation.

The reasons for regarding ecology and physiology as essentially the same have been given elsewhere, and need not be repeated here. An endeavor has been made to give the various parts of this vast field their proper importance. Since ecology and physiology are merged, it is manifestly impossible to give to either what would be regarded as a complete treatment by a specialist in either line. No attempt has been made to touch all the points in each, but it is thought that nothing really fundamental has been omitted.

The book is intended for use with classes in second-year botany in college and university. In manuscript form, it has been in such use for two years with good results. Although the amount of laboratory and field work is large, it is possible to accomplish all of it in a course requiring 6-8 hours of laboratory time each week. This can be done only by careful planning on the part of both instructor and student, and for this reason the following suggestions are offered as aids.

The instructor will find it imperative to plan in advance for the experiments for the whole year, in order that plants may be ready as needed. Seeds and fruits for the study of migration should be collected in the fall. Shade tents, water-content series, and comiv PREFACE

petition cultures must also be prepared early in the year. Types of hydrophytes, xerophytes, etc., should be grown in the plant-house in so far as possible. Students should be instructed to make duplicate plantings of all plants to be used in order to make sure of an adequate supply at all times. It has also been found desirable to teach the students the use of the paraffin method of embedding tissues, thus saving much time and securing better results. The work on adaptation to water and light is best carried on in the form of joint experiments, in which each student is assigned a definite part. In the experiments much use has been made of the common sunflower. This is on account of the ease with which it may be secured and grown, but w T hen a larger choice is possible other plants may often be substituted to advantage.

In just as far as possible, the work of the student should be among plants out-of-doors. This is imperative in the chapters on vegetation, and is very desirable in all cases where it is feasible, even in the study of plant functions. For vegetation work, the knowledge of the more important genera and species of the several formations is indispensable. If the student does not already have this knowledge, the names should be furnished him by any desirable method, without taking the time necessary for identification.

A bibliography has not seemed necessary and has not been given. A fairly full list of the more important works is found in " Research Methods." Apart from the latter, Pfeffer's "Pflanzenphysiologie," MacDougaPs "Text-book of Plant Physiology," Sach's "Text-book of Botany/' Vines' "Lectures on the Physiology of Plants," and Kerner's " Pflanzenleben " have been frequently consulted in the preparation of the text.

Grateful acknowledgment is made of the kindness of Dr. C. E. Bessey, Dr. D. T. MacDougal, and Dr. Edith Clements in reading and criticizing the text. The author is also indebted to Dr. Edith Clements for many drawings, and for the use of cuts from "The Relation of Leaf Structure to Physical Factors," and to Mr. R. J. Pool and Mr. A. W. Sampson for the loan of several photographs.

Frederic Edward Clements.

The University of Nebraska, March 1907.

Chapter I Stimulus And Response Page

1. Fundamental Relations 1

2. The Nature of Stimuli 1

3. The Kinds of Stimuli 3

4. The Nature of Response 3

5. Adjustment and Adaptation 4

6. Kinds of Adjustment 5

7. Normal and Abnormal Adjustment 5

Chapter II The Water Of The Habitat

8. Relation of the Plant to Water 7

9. The Nature of Water Stimuli 7

10. Water Content 8

11. Influence of other Factors upon Water Content 9

12. Available and Non-available Water Content 9

13. Soil Samples 10

14. Computation of Water Content 11

15. Time of Water Content Readings 12

16. Location of Readings 12

17. Depth of Samples 12

Experiment 1. Measurement of Water Content 13

18. The Determination of Available Water 13

19. Chresard of Habitats 14

Experiment 2. Determination of Available Water 14

Modifying Factors

20. Influence of Soil upon Water Content 15

21. Origin and Structure 16

22. Water Capacity 17

v vi CONTENTS

PAGE

23. Chemical Nature of Soils 18

24. Air Content 19

25. Determination of Soil Properties 19

Experiment 3. Porosity and Rate of Evaporation 20

26. Influence of Precipitation upon Water Content 21

27. Measurement of Rainfall 21

28. Physiography , 22

29. The Influence of Slope 23

30. The Influence of Surface 23

31. The Influence of Climatic Factors 24

32. Humidity 24

33. Modifying Influence of Temperature and Wind 25

34. Influence of Pressure and Physiographic Factors 26

35. Effect of Climate and Habitat 27

36. Measurement of Humidity 27

37. Sling and Cog Psychrometer 28

38. Making a Reading , 29

39. Use of Humidity Tables 30

Experiment 4- Measuring Humidity 30

40. Method of Habitat Study 30

41. Choice of Stations 31

42. Constant Factors 31

43. Simultaneous Readings 31

44. Point and Hour Readings 33

45. Records 33

46. Kinds of Curves 34

47. Combinations of Curves 34

48. Plotting Curves 35

49. Intervals for the Different Factors 36

Experiment 5. Determining the Physical Factors of Habitats. . 36

Chapter III Adjustment To Water

50. Responses to Water Stimuli - 38

Absorption

51. General Relations 38

52. The Form of Roots 39

53. Primary Regions of the Root 39

54. Detailed Structure 40

55. Origin and Structure of Root-hairs 42

56. Effect of Water Content upon Root-hairs and Roots 43

Experiment 6. Structure of the Root and Formation of Root-hairs. 44

Experiment 7. Hydrotropism 44

CONTENTS vii

1'AfiE

57. Imbibition j I

Experiment 8. Water of Imbibition 45

58. Osmosis 45

,">!). ( )smosis in Root-hairs 46

60. Influence of Soluble Salts 47

Experiment 9. Demonstration of Osmosis 47

Experiment 10. The Effect of Soluble Salts 47

61. Effect of Protoplasm upon the Absorption of Soluble Salts 48

62. Diffusion 48

Experiment 11. Diffusion in Liquids and in Tissues 49

63. Turgidity 49

Experiment 12. Demonstration of Turgidity 50

Transport

64. General Nature 50

65. Types of Stem Structure 51

66. Stem Structure of an Herbaceous Dicotyledon 52

67. Stems of Monocotyledons 53

68. Structure of Woody Stems 53

69. Functions of the Stem 54

Experiment 13. Structure of Stems 54

70. The Upward Movement of the Water 54

71. Causes of the Movement 55

Experiment 14- Pathway and Rate of Movement 56

Transpiration

72. The Structure of a Representative Leaf 56

73. The Chlorenchym 57

74. The Reduced Bundles 58

Experiment 15. Structure of a Leaf 58

75. Diffusion in the Leaf 58

76. Transpiring Surface 59

Experiment 16. Measurement of the Actual Transpiring Surface . 59

77. Structure and Position of Stomata 60

78. The Functions of Stomata 61

79. Movements of Guard-cells .• 61

Experiment 17. Movement of Guard-cells 62

Experiment 18. Position of Stomata and Water Loss 62

80. The Influence of Physical Factors upon Transpiration 63

81. The Measurement of Transpiration 64

82. Measuring Transpiration in the Field ". 65

Experiment 19. Influence of Factors upon the Rate of Transpiration 65

83. The Amount of Transpiration in Plants 66

84. Relation between Transpiration and Absorption 68

85. Compensation for Increased Transpiration 68 vi CONTENTS

PAGE

23. Chemical Nature of Soils 18

24. Air Content 19

25. Determination of Soil Properties 19

Experiment 3. Porosity and Rate of Evaporation 20

26. Influence of Precipitation upon Water Content 21

27. Measurement of Rainfall 21

28. Physiography 22

29. The Influence of Slope 23

30. The Influence of Surface 23

31. The Influence of Climatic Factors 24

32. Humidity 24

33. Modifying Influence of Temperature and Wind 25

34. Influence of Pressure and Physiographic Factors 26

35. Effect of Climate and Habitat 27

36. Measurement of Humidity 27

37. Sling and Cog Psychrometer 28

38. Making a Reading 29

39. Use of Humidity Tables 30

Experiment 4- Measuring Humidity 30

40. Method of Habitat Study 30

41. Choice of Stations 31

42. Constant Factors 31

43. Simultaneous Readings 31

44. Point and Hour Readings 33

45. Records 33

46. Kinds of Curves 34

47. Combinations of Curves 34

48. Plotting Curves 35

49. Intervals for the Different Factors 36

Experiment 5. Determining the Physical Factors of Habitats. . 36

CHAPTER III ADJUSTMENT TO WATER

50. Responses to Water Stimuli - 38

Absorption

51. General Relations 38

52. The Form of Roots 39

53. Primary Regions of the Root 39

54. Detailed Structure 40

55. Origin and Structure of Root-hairs 42

56. Effect of Water Content upon Root-hairs and Roots 43

Experiment 6. Structure of the Root and Formation of Root-hairs. 44

Experiment 7. Hydrotropism 44

CONTENTS vii

PAGE

57. Imbibition 44

Experiment 8. Water of Imbibition 15

58. Osmosis 45

59. Osmosis in Root-hairs 46

GO. Influence of Soluble Salts 47

Experiment 9. Demonstration of Osmosis 47

Experiment 10. The Effect of Soluble Salts 47

61. Effect of Protoplasm upon the Absorption of Soluble Salts 48

62. Diffusion 48

Experiment 11. Diffusion in Liquids and in Tissues 49

63. Turgidity 49

Experiment 12. Demonstration of Turgidity 50

Transport

64. General Nature 50

65. Types of Stem Structure 51

66. Stem Structure of an Herbaceous Dicotyledon 52

67. Stems of Monocotyledons 53

68. Structure of Woody Stems 53

69. Functions of the Stem 54

Experiment 13. Structure of Stems 54

70. The Upward Movement of the Water 54

71. Causes of the Movement 55

Experiment 11^. Pathway and Rate of Movement 56

Transpiration

72. The Structure of a Representative Leaf 56

73. The Chlorenchym 57

74. The Reduced Bundles 58

Experiment 15. Structure of a Leaf 58

75. Diffusion in the Leaf 58

76. Transpiring Surface 59

Experiment 16. Measurement of the Actual Transpiring Surface. 59

77. Structure and Position of Stomata 60

78. The Functions of Stomata 61

79. Movements of Guard-cells : 61

Experiment 1 7. Movement of Guard-cells 62

Experiment 18. Position of Stomata and Water Loss 62

80. The Influence of Physical Factors upon Transpiration 63

81. The Measurement of Transpiration 64

82. Measuring Transpiration in the Field ". 65

Experiment 19. Influence of Factors upon the Rate of Transpiration 65

83. The Amount of Transpiration in Plants 66

84. Relation between Transpiration and Absorption 68

85. Compensation for Increased Transpiration 68 vni CONTENTS

86. Details of the Adjustment 69

Experiment 20. Pathway of Adjustment 70

Chapter IV Adjustment To Light

87. Relations of the Plant to Light 71

88. The Nature of Light Stimuli 72

89. Measurement of Light 72

90. Making a Standard 73

91. Making Readings 74

92. Comparison with the Standard 75

93. Causes of Variation in Light Intensity 75

94. The Effect of Time 75

95. The Effect of Altitude 76

Experiment 21. Measuring Light Intensity 77

96. Reception and Absorption of Light 77

97. The Amount Absorbed 77

Experiment 22. Epidermis and Leaf Prints 78

98. The Production of Chlorophyll 79

99. The Nature of Chlorophyll 79

100. The Influence of Darkness 80

Experiment 23. Influence of Light and Darkness 81

101. Photosynthesis 81

102. Absorption and Diffusion of Carbon Dioxide 81

103. Chemical Changes during Photosynthesis 82

Experiment 24. Dependence of Photosynthesis upon Aeration

and Light 83

104. Measurement of Photosynthesis 83

Experiment 25. Relation of Photosynthesis to Sun and Shade. . 83

105. Translocation 83

Experiment 26. Translocation 84

106. Storage of Food Material 84

Experiment 27. Storage Tissues 85

107. Influence of Light upon the Number and Position of Chlorop lasts . 85

Experiment 28. Arrangement of Chloroplasts 87

108. Movement of Stems and Leaves 87

109. Phototropism 87

Experiment 29. Phototropic Movements 89

110. Nyctotropism 89

Experiment 30. Nyctotropic Movements 89

Chapter V Adjustment To Temperature

111. Relations of Plants to Temperature 90

112. The Measurement of Temperature 91

CONTENTS ix

PAGE

1 13. Soil Temperatures 92

114. Plant Temperatures 92

Experiment 31. Temperatures of Plant and Habitat 93

115. Variations of Temperature 94

116. The Influence of Other Factors 95

117. Favorable and Unfavorable Temperatures 95

118. Freezing 96

Experiment 32. Effects of Freezing 97

119. The Sum of Temperatures 97

120. Influence upon Vegetation 98

121. Digestion 99

122. Chemosynthesis of Digested Materials 100

123. Respiration 101

124. Fermentation 102

125. Germination 102

Experiment 33. Digestion and Respiration in Seeds 103

126. Nutrition of Hysterophytes 104

127. Kinds of Parasites 104

Experiment SJf.. Nutrition of Representative Hysterophytes 105

129. Growth of Tissues and Organs 106

Experiment 35. Regions of Growth 107

130. Conditions that Influence Growth 108

131. The Amount and Rate of Growth 108

132. Regions of Greatest Growth in Various Organs 109

Experiment 36. Influence of Temperature, Water and Light upon

Regions of Growth 110

133. Rhythm of Growth 110

134. The Age of a Plant 112

135. Reproduction 112

136. Propagation 113

137. Propagules of Flowering Plants 114

138. Stems as Propagules 114

Experiment 37. Propagules 115

139. Sexual Reproduction 115

140. Production of Pollen 116

Experiment 38. Amount of Pollen 118

141. Protection of Pollen 118

142. Structural Protection 119

143. Protection by Movement 120

144. Seasonal Protection 121

Experiment 39. Protection of Pollen 122

145. Disposition of the Stamens and Pistils 122

Experiment 4.0. Grouping of Stamens and Pistils 123

146. Source and Destination of Pollen 124

147. Cross-pollination 125

148. Pollination by Insects 126 x CONTENTS

PAGE

149. Self-pollination 127

Experiment 41 . Pollination 128

150. The Period of Flowering 128

151. Time of Daily Flowering 130

Experiment 42. Time of Flowering 131

152. Fructification 131

153. Fleshy Fruits 131

154. Dry Fruits 132

155. Movements of Fruits 132

Experiment 43. Kinds of Fruits 133

Chapter VI Adjustment To Gravity, Contact And Shock

156. The Relation of the Plant to Gravity 135

157 . Geotropism 135

158. Cause and Reaction 137

159. Region of Curvature 138

160. Ecological Significance of Geotropism 139

Experiment 44- Geotropism 139

161. Response to Contact. 141

Experiment 45- The Behavior of Tendrils 142

162. Response to Shock 142

Experiment 46. Response to Shock 143

Chapter VII Adaptation To Water

163. The Relation of Structures to Water 144

164. Adaptation to a Small Water Supply 144

165. Decrease of Water Loss through Leaf Position 145

166. Decrease through the Rolling of the Leaf . 145

167. Reduction of Leaf or Stem '. 147

168. Changes of the Epidermal Cells 147

169. Modifications of the Stomata 148

170. Changes in the Chlorenchym 150

171. Increase and Storage of Water Supply 151

172. Adaptation to Excessive Water Supply 152

Experiment 47 '■ Experimental Adaptation to Water 153

173. Types of Plant Body 154

174. Types Produced by Adaptation to Water 155

175. General Features of Xerophytes 156

176. Types of Leaf Xerophytes 156

177. Normal Leaf Xerophytes 157

178. Storage Leaves , 158

CONTENTS xi

PAGE

179. Lanate Leaves 159

Experiment 4.S. Study of Normal Leaf Xerophytes 159

180. Other Leaf Xerophytes 159

Experiment Jfi. Study of Xerophytic Leaves 162

181. Stem Xerophytes 162

182. Types of Stem Xerophytes 162

Experiment 50. Form and Structure of Stem Xerophytes 164

183. Mesophytes 164

Experiment 51. Comparison of Mesophyte and Xerophyte. ... 165

184. Hydrophytes 165

185. Amphibious Plants 166

Experiment 52. Structure of Amphibious Plants 167

186. Floating Plants 167

Experiment 53. Structure of Floating Plants 168

187. Submerged Plants 168

Experiment 54- Structure of Submerged Plants 168

188. Bog Plants 168

Experiment 55. Study of Water Content Types 170

Chapter VIII Adaptation To Light

189. The Relation of Organs to Light 171

190. Influence of the Chloroplasts 171

191. Modifications of the Chlorenchym 172

192. Sponge Tissue 174

193. Palisade Tissue 176

194. Changes of the Epidermis 177

195. The Form of Leaves 178

196. Changes of Outline, Size and Thickness 178

197. The Form of Stems 179

Experiment 56. The Production of Adaptations to Light 181

198. Types of Leaves as Determined by Light 182

199. Sun Plants and Shade Plants 183

Experiment 57. Sun and Shade Forms in Nature 184

Chapter IX The Origin Of New Forms

200. The Law of Evolution 185

201. Stability and Plasticity 185

202. Constant and Inconstant Forms 186

203. Origin by Descent before Darwin 187

204. Darwin and the Origin of Species 188

205. Evolution after Darwin 189 xii CONTENTS

PAGE

206. Fundamental Methods of Evolution 191

207. Origin by Adaptation 192

208. Origin by Variation 195

209. Origin by Mutation 196

210. Origin by Hybridation 197

Experiment 58. The Occurrence of New Forms in Nature 198

211. Natural Selection 198

212. Isolation 199

213. Polygenesis 199

214. Experimental Evolution 201

Chapter X Methods Of Studying Vegetation

215. The Study of Vegetation 202

216. The Quadrat 202

217. Kinds of Quadrats 203

218. Marking out Quadrats 204

219. The List Quadrat 204

220. Abundance 205

221. The Chart Quadrat 205

222. Making Quadrat Charts 206

223. The Permanent Quadrat 208

224. The Denuded Quadrat 209

225. Transects 210

226. The Line Transect 210

227. The Belt Transect 211

228. The Migration Circle 212

229. Formation Maps 213

Chapter XI The Plant Formation

230. The Nature of Formations 215

231 . Recognition of Formations 216

232. Relation between Habitat and Formation 218

233. The Historical Factor 219

234. Development and Structure 219

235. Structure of the Formation 221

237. Principal and Secondary Species 222

238. Aspects 223

Experiment 59. Study of Abundance and of Aspects 224

239. The Parts of a Formation: the Consocies 225

240. The Society 226

CONTEXTS Xlli

PAGE

241. The Community 227

242. The Family 228

Experiment 60. The Structure of a Formation 229

Experiment 61. Layered Formations 230

244. Classification 230

245. Classification by Habitats 231

246. Types of Formations 232

247. Developmental or Physiographic Classification 233

248. Regional Classification 234

249. Open and Closed Formations 235

250. Mixed Formations 235

Experiment 62. Comparison of Formations 236

Chapter XII Aggregation And Migration

251. Aggregation 237

252. Simple Aggregation 237

253. Mixed Aggregation 239

Experiment 63. Study of Families and Communities 240

254. Migration 240

255. Mobility 241

256. Organs of Dissemination 241

257. Modifications for Migration 242

258. Influence of Seed Production 243

259. Position of Disseminules 244

260. The Agents of Migration 244

261. The Work of Migration Agents 248

Experiment 64- Modifications for Migration 249

262. The Direction of Migration 249

Experiment 65. Amount and Direction of Migration 250

Chapter XIII Competition And Ecesis

263. Competition 251

264. The Struggle for Existence 251

265. The Nature of Competition 252

266. The Factors Involved 253

267. Competition for Water and Light 253

268. Competition between Parents and Offspring 254

269. Competition between Different Species 255

270. Influence of Vegetation Form and Habitat Form 256

271. The Effect of Position 256 xiv CONTENTS

PAGE

272. Vegetation Pressure 257

273. The Results of Competition 258

274. The Study of Competition 259

275. Competition Cultures 259

276. Competition Quadrats 261

Experiment 66. Competition 261

278. The Factors in Ecesis 262

279. Germination of the Seed 263

280. The Effect of Habitat 264

281. Adjustment to the Habitat 265

Experiment 67. Influence of Habitat Form upon Ecesis 265

282. Barriers 265

283. Physical and Biological Barriers 266

284. Influence of Barriers 266

285. Distance 267

286. Endemism 268

Experiment 68. Barriers and Endemism 269

Chapter XIV

287. Invasion 270

288. The Manner of Invasion 270

289. Invasion at Different Levels 272

290. Kinds of Invasion 272

291. Indigenous and Derived Species 273

Experiment 69. Invasion 273

292. Succession 273

293. Kinds of Succession 274

294. Primary Successions 275

295. Succession in Colluvial Soils 276

296. Succession in Alluvial Soils 277

297. Succession in iEolian Soils 278

298. Secondary Successions 278

299. Succession in Eroded Soils 279

300. Succession in Flooded Soils 280

301. Successions Due to Man 280

302. Successions in Burned Areas 281

303. Succession in Lumbered Areas 282

304. Succession by Cultivation 282

305. Reactions of Plants upon the Habitat 282

306. The Laws of Succession 284

307. The Study of Successions 286

308. Method of Alternating Areas 286

309. The Relict Method 287

Experiment 70. The Study of a Secondary Succession 288

CONTENTS xv