Slcrilily 139 



sterile plants inler se. In his earlier cultures he had found that 

 the self-sterile plants were consistently cross-fertile; that is, there 

 might ])e quite a group of individuals each one of which would 

 set seed when pollinated from any of the other individuals, but 

 would not set seed when self-pollinated. East concluded that, 

 when one is deahng with self-sterile plants (those lacking the 

 gene for self-fertility), pollen is effective only when it comes from 

 a source that has a somewhat different germinal constitution from 

 that of the ovules. If, therefore, a group of self-sterile plants is 

 consistently cross-fertile, it is to be concluded that every individual 

 of this group differs in some degree from every other individual 

 of the group with respect to a certain set of factors that is effective 

 in this connection. If this assumption is correct, it should be 

 possible in the later generations to obtain groups of individuals all 

 of the same genotype with respect to the effective factors. The 

 individuals of any such group should then be cross-sterile with 

 reference to each other. East actually obtained such groups 

 among the later generations, thus supporting his assumptions on 

 the relations of self-sterile plants inter se. An exact factorial 

 analysis has not been possible as yet, but it is plainly a matter of 

 Mendelian inheritance, and the general mechanism is rather 

 clearly indicated. 



Much work remains to be done on the physiology of self- 

 sterility, although a few interesting findings have already been 

 made on that matter. It has been discovered (at least for a great 

 many cases of self-sterility) that the problem is tied up with the 

 growth of the pollen tube. Own pollen, quite healthy and func- 

 tionable on foreign stigmas, will also germinate and start pollen 

 tubes on own stigmas. Such tubes, however, are for some reason 

 not successful in reaching the ovules. Assumptions were made, 

 by various authors, that own stigmas poison own pollen tuljes 

 or furnish them with inadequate nutrition. One author (Moore 

 9) has assumed that own stigmas provide own pollen tubes with 

 too good nutrition, so that the tubes fatten but do not elongate 

 (just as the hypha of a fungus will elongate more on a poor nutri- 

 tive medium than on a good one). East (5) himself has done some 

 critical work, however, that indicates the inaccuracy of all of the 

 foregoing assumptions, and reveals an interesting phenomenon 



