220 BOOKS AND CURRENT LITERATURE 



more than ten species. The second column shows the number of species 

 recognized by Thurber, and illustrates the increase in knowledge of the 

 state flora; the third column, giving the species in the new Gray's Manual, 

 is a partial indication of the difference of development which these leading 

 genera have attained on the two sides of the continent. That this large 

 increase is not the result of reckless species-making is evident from the 

 fact that but four new species are proposed in the work, and fewer pre- 

 viously described varieties raised to specific rank, while a considerable 

 number of both species and varieties are reduced to synonomy. The 

 lack of a comprehensive manual of the Californian flora has been 

 nowhere more painfully evident than in the study of the grasses, and it 

 will prove a great satisfaction to all students to have this want so satis- 

 factorily supplied. — S. B. Parish. 



Foliar Periodicity in the Tropics. — Volkens has published 1 a 

 detailed series of observations on the fall and renewal of foliage in 100 

 tropical trees growing in the Buitenzorg Garden, together with a digest 

 of his own results and those of Wright, obtained in Ceylon. The periodic 

 phenomena of tropical foliage have never before been treated as a physio- 

 logical problem, and Volkens has accordingly done much toward clarify- 

 ing the subject, in spite of the confessed inconclusiveness of his results. 

 He finds that the majority of tropical trees have a definite annual periodic- 

 ity of leaf behavior, which however differs greatly between different spe- 

 cies both in its character and in the time of its occurrence. A minority 

 of trees show a continuous foliar activity. In' very many species there 

 mi 1 differences of foliar behavior between different individuals, different 

 branches of the same individual, and individuals of different ages, 

 although such differences are usually due merely to a slight lack of syn- 

 chronism. Volkens finds that the considerable differences of rainfall 

 between winter and summer at Buitenzorg do not bring the activities of 

 any majority of trees into unison, although he acknowledges that the 

 monthly fluctuation of rainfall does not mean an equal fluctuation of 

 soil moisture. He finds the annual temperature curve too slight in its 

 amplitude to account for any of the foliar phenomena, and he dismisses 

 as untenable the theory of A. M. Smith that fluctuation in the salt content 

 of the soil water is the determining factor. An examination of the starch 

 content of twigs and stems in newly foliated and in defoliated trees 



1 Volkens, G., Laubfall unci Lauberneuerung in den Tropen. Pp. 142. Berlin, 

 Borntraeger, 1912. (Mk. 3.80.) 



