Current Literature 83 



daily gain in weight for leaves from vines 5 to 8 years old was 9.3 

 per cent, while the average daily gain for leaves of vines 20 to 25 

 years old was 1.9 per cent. The investigator also found by experi- 

 ment that there was a decrease in the rate of respiration with 

 increase in age of the plant on which the leaf was borne; also a 

 probable increase with age in the number of stomata and a de- 

 crease in the size of the stomatal aperature; and a probable 

 decrease with age in the size of the palisade cells. 



The author concludes that certain tissues of the plants studied 

 exhibit semle degeneration comparable to that in animal tissues. 

 This is shown graphically by two curves, one showing the decrease 

 in the size of vein islets and the other showing the senile decrease 

 in the rate of growth of guinea pigs. The curves disclose a re- 

 markable correspondence in the two phenomena. It is interest- 

 ing to note how the pendulum swings! More than 100 years ago, 

 Knight made this statement: "I am therefore much disposed to 

 attribute the diseases and debility of old age in trees to an in- 

 ability to produce leaves which can efficiently execute their 

 natural office. It is true that leaves are annually reproduced, 

 and, therefore, annually new, but there is, I conceive, a very 

 essential difference between the new leaves of an old and of a 

 young variety." Since that time practically all the men who have 

 investigated the problem asserted that Knight's conclusion was 

 wrong for the reasons stated in the first paragraph of this review. 

 The present author, however, is apparently the only one who 

 reached his conclusion through a mass of experimental data. 



Some 20 pages of this very interesting paper are given to a 

 discussion of the causes of senile changes. After showing that 

 most of the theories of animal physiologists are inadequate — at 

 least as appHed to plants > — , the author develops his theory that 

 senility is due to the progressive decrease, as age advances in the 

 permeability of the protoplasm, thus producing an increasing 

 degree of inability to absorb food materials from without as well 

 as an increasing retention of toxic waste products within the cell. 



C. D. H. 



Ueber das Treihen der einheimischen Bdume, speziell der Buche. 

 By G. Klebs. Heidelberg. 1914. Pp. 166. 



This work is of peculiar significance in the theoretical field, 

 but, nevertheless, it is of importance to the forester, as it brings 



