176 BOTANICAL GAZETTE [march 



proposed different auxiliary suppositions. And since the possi- 

 bility is acknowledged that mutability may be far more widely 

 spread within this group than we now know, such suppositions 

 must not be of a limited nature, but applicable to large divisions of 

 the vegetable kingdom. Kearney, in studying the mutations of 

 the Egyptian cotton, comes to the conclusion that these and other 

 mutations might be the result of crosses between remote ancestors, 

 but that these crosses have left no other traces in their descendants 

 than "the disturbance of germinal equilibrium, which manifests 

 itself in the production of mutants."" It is not very clear how 

 this supposition is to bring the problem nearer to its solution. 



In a recent article in this journal," Jeffrey takes an opposite 

 position. He assumes that the ancestral crosses have left another 

 visible trace in their descendants, which is the partial sterility of 

 their sexual cells. It is a well known fact that many hybrids have 

 partially sterile pollen, while acknowledged species have, as a rule, 

 only fertile pollen grains. Jeffrey assumes this rule to be without 

 exceptions, but does not adduce any arguments in favor of this 

 hypothesis. It is difficult to judge the value of an argument so 

 long as the facts upon which it rests have not been submitted to 

 criticism. But I might suggest that it seems rather hard to recon- 

 cile this view with the fact that in angiosperms three of the four 

 megaspores are usually sterile, while only one produces an embryo 

 sac. Are we to deduce from this fact, in connection with Jef- 

 frey's hypothesis, that all angiosperms are hybrids, at least on 

 the maternal side ? 



Numerous special arguments could be adduced. It may sufl&ce, 

 however, to point out the genus Carex, in some of the best species 

 of which the pollen is in the same condition, three of the grains of 

 each tetrad being sterile and only one fertile. '^ Every single grain 

 of the ripe pollen is a tetrad, showing the very reduced rudimentary 

 remnants of three of its cells as a flattened investment of the 

 fertile one. 



"Kearney, T. H., Mutation in Egyptian cotton. Jour. Agric. Research 2:287- 

 302. 1914. 



"Jeferey, E. C, Spore conditions in hybrids and the mutation hypothesis of 

 DeVries. Bot. Gaz. 38:322-336. 1914. 



« JuEL, H. O., Die Entwickelung der Pollenkomer bei Carex. Jahrb. Wiss. Bot. 

 35:649-656. 1900. 



