CONTENTS 



PAGE 



Senile changes in animals ' 281 



Senile changes in physiological activities 282 



Deterioration evident from the beginning 282 



Deterioration appearing later in life 284 



Senile changes in the structure of animal organs 285 



Senile changes in the structure of animal cells 287 



Changes evident from the beginning 287 



Changes appearing later 287 



Investigations on senility in plants : general 288 



Review of hterature 288 



Importance and significance of the problem 289 



Investigations on senile changes in leaves of Vitis vulpina L. and 



certain other plants 290 



Plan of investigation 290 



Collection and preparation of material 291 



Influence of certain factors on venation 293 



Uniformity in size of vein islets on different parts of a leaf. . . . 294 



Influence of size of leaf blade on size of vein islets 294 



Influence of thickness of leaf on size of vein islets 296 



Influence of such differences in light as are found in nature 



on the size of vein islets 297 



Uniformity in size of vein islets in each vine 298 



Comparison of the size of vein islets in plants of different ages, 



in Vitis vulpina 300 



Size of vein islets of plants grown under field conditions .... 300 

 Size of islets in leaves of cuttings grown under identi- 

 cal conditions 312 



Comparison of the venation of immature leaves 314 



Method for determining approximate age by measurement of 



veinage 317 



Comparison of size of vein islets in plants of different ages, in 



Vitis bicolor and certain other plants 318 



Size of vein islets in Vitis bicolor Le Conte 318 



277 



