﻿CURRENT LITERATURE 



NOTES FOR STUDENTS 



Age changes in leaves. — An interesting and important paper by Bene- 

 dict 1 is an attempt to answer- the question whether general progressive age 

 changes occur during the vegetative life of a woody perennial, and constitutes, 

 so far as the reviewer's knowledge goes, the first positive evidence based on exact 

 observation for an affirmative answer to the question. The author approaches 

 his subject with a brref resume of the physiological and morphological age 

 changes in animals, pointing out that much more attention has been paid to 

 the phenomena of senescence in animals than in plants, there being as regards 

 plants practically no really conclusive data at hand. He emphasizes both 

 the scientific and the practical importance of the question whether plants 

 actually grow old, and notes that in view of the great differences in length of 

 life in different animal species the very great length of life attained by certain 

 trees does not constitute any real answer to the question. 



As the chief material for his own study of senescence in plants the author 

 has chosen the leaves of the wild grape (Viiis imlpina L.) for various excellent 

 reasons noted in the paper, and his observations concern primarily the size of 

 the aggregations of photosynthetically active cells, the vein islets in the meshes 

 of the network of veinlets, or in other words the size of these meshes. Briefly 

 stated, the chief results of the paper are these: The size of the vein islets is 

 essentially the same in different regions of the same leaf and in leaves of differ- 

 ent size and thickness from plants of the same or nearly the same age, and differs 

 but slightly with ordinary differences of light and shade. A comparison of 

 minimum and maximum areas of the vein islets in different leaves of the same 



themselves. All these facts indicate that the size of the vein islets is governed 

 by some internal characteristic of the plant as a whole, or more specifically 

 of the meristematic tissue. The ground being thus cleared, the next step is 

 the comparison of the size of the vein islets in the leaves of plants of different 

 ages, age being determined by the number of rings in the main trunk or in 

 some extreme cases by the size of the trunk. The very extensive series of 

 measurements show beyond question that the size of the vein islets is greatest 

 in the youngest plants and undergoes a progressive decrease v th 1 i ng 

 age. This difference in size holds good for immature as well as for mature 



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