278 Contents 



PAGE 



Comparison of size of vein islets in Tecoma radicans L 321 



Size of vein islets in several kinds of trees 322 



Size of vein islets in leaves of several varieties of fruits 



propagated bj^ cuttings 324 



Conclusions regarding the size of vein islets as evidence of the 



occurrence of true senility in perennial plants 325 



Comparison of photosj^nthetic acti\dty in leaves of young and of old 



plants 330 



Conclusions regarding relative rate of carbohydrate production 

 in the leaves of j^oung and of old \dnes of Mtis vulpina 



and Ampelopsis veitchii 333 



Rate of ehmination of carbon dioxide in picked leaves of Vitis vulpina 



of different ages 333 



Imbibition of water by powdered leaves of young and of old vines .... 338 



Degree of imbibition with distilled water 338 



. Relative acidity of the young and the old powdered leaves 339 



Imbibition after neutralization 340 



Other evidences of senility 341 



Comparison of numbers of stomata in leaves of young and of old 



vines of Yitis vulpina 342 



Comparison of sizes of palisade cells in leaves of 3'oung and of old 



vines of A^itis vulpina 344 



Relative mass of nucleus and cytoplasm in cells of the leaf in 



young and in old vines of Vitis vulpina 345 



Summary ■ 346 



Discussion 346 



Significance of senile changes to the problem of the running-out 



of vegetatively propagated fruits 347 



Bearing of these facts on theories of senility 353 



Theories of senility 355 



Decreasing permeability as an explanation of some observed 



senile degenerations 361 



Acknowledgments 365 



BibHography. 365 



