116 BOOKS AND CURRENT LITERATURE 



power for water than that from young plants, and the leaf powder 

 from young plants is markedly more acid than that from old plants. 

 Stomatal frequency is much greater for leaves of old plants than for 

 those of young ones, but the average length of stomatal opening is 

 greater for young plants. The average length of palisade cells was found 

 to be 12.2 micra for vines with 5 rings, and 10.3 micra for vines with 

 20 rings. Finally, some evidence is presented suggesting that the 

 volume ratio of cytoplasm to nucleus in leaf cells is greater for young 

 than for old plants. 



In many respects, therefore, plant senility alterations appear to 

 parallel the corresponding changes recorded for animals, and it is once 

 again indicated that plants and animals are essentially alike in their 

 general protoplasmic characters. The physico-chemical explanation of 

 senile change is not yet apparent, however. Benedict emphasizes a 

 decreased permeability of the protoplasm of cells of old plants, as a 

 possible cause of age alteration. 



To the reviewer, the criterion of size of intervenal areas appears to 

 promise much in connection with the comparison of different plants as 

 related to their surroundings. The possible influence of environmental 

 conditions on vein islet size in the same plant form should receive 

 attention, and different forms should be compared by this criterion. — 

 B. E. Livingston. 



