Varietäten, Descendenz, Hybriden. 131 



Pritchard, F. J., C hange of sex in hemp. (Journ. of Heredity 

 VII. p. 325—329. 1916.) 



The difference of opinion regarding the effect of external Sti- 

 muli upon sex ratios had led the writer to investigate the following 

 questions: 



1. Can sex ratios of dioecious plants be altered by modifying 

 conditions external to their germ cells? 



2. Is the alteration thus obtained limited to individuals of one sex? 



3. How do the results harmonize with the Mendelian conception 

 of sex determination? 



Owing to certain circumstances the results of the writers in- 

 vestigations are limited to 1909 and 1914; in both years disturban- 

 ces of the plant's physiological equilibrium were induced by the 

 removal of flowers and vegetative parts; in 1909 only also by the 

 injection of chemical substances into the stem. Alteration of sex 

 occurred under several different treatments. Either covering the 

 top with a Manila bag or injecting into the stem a Solution of dex- 

 trose, maitose, glucose, asparagin or pyridin was accompanied by 

 a modification of sex. In each instance, however, the removal of 

 parts constituted a part of the treatment. In fact the removal of 

 parts was the only factor common to all the sex-developingresponses. 

 Hence it was probably the chief cause of sex alteration. While only 

 a few male plants produced pistils, they constituted 14 to 21°/o of 

 the total number of males reproducing flowers after the Operation. 

 It is quite probable that if the proper Stimulus were used pistil 

 formation could be induced in all the males. The females were very 

 responsive to the stimulating effect of flower removal. In fact in the 

 second year's experiments every female operated upon produced 

 an abundance of stamens. 



The results do not seem to support the theory that sex is 

 wholly a matter of zygotic Constitution — one dose or amount of 

 an inherited sex factor producing one sex and two the other — but 

 indicate that both males and females are potential hermaphrodites, 

 as believed by Darwin and Strasburger. 



M. J. Sirks (Bunnik). 



Sinnott, E. W., Comparative rapidity of evolution in 

 various plant tj^pes. (American Naturalist. L. p. 466— 478. 1916.) 



The summary of this paper, as given by the writer, runs as 

 follo WS : 



1. The most recently evolved element in the fioras of temperate 

 North America and of Europe, as determined by a study of 

 the indigenous endemic genera, is composed almost entirely of 

 plants which are herbaceous in habit. 



2. Herbs tend to be grouped in fewer and larger genera and 

 families than woody plants. 



3. It is therefore concluded that herbaceous plants, presumably 

 because of the brevity of their life cycle and the rapid multiplica- 

 tion of generations consequent thereto, are in most cases under- 

 going evolutionary development much more rapidly than are trees 

 and shrubs. 



4. From this conclusion are drawn inferences as to the origin 

 of the herbaceous habit and the antiquity of the Angiosperms. 



These inferences are characterized by these sentences: 



It is probable that in order to have developed their great num- 



