CHAPTER X 



STERILITY 



The subject of sterility in plants is only in part a matter of 

 genetics. Many of the problems involved can be solved only by 

 the physiologist, ecologist, or cytologist. Some phases of the 

 subject, however, have been rather successfully interpreted in 

 terms of genetics. Tentative outlines of the general subject will 

 be presented, merely to show what parts of the problem are being 

 attacked by the geneticist. 



First of all, sterility might be classified in terms of the effects 

 produced : 



A. Sterility. Complete failure of the sex act. 



B. Semi-sterility. Failure of part of the pollen, or part of 

 the ovules, or part of both. 



C. Self-sterility. Pollen and ovules functional in cross- 

 fertilization but not in self-fertilization. 



A more comprehensive classification might then be arranged 

 on the basis of cause, although such a classification, in our present 

 state of knowledge, must be rather vague and uncertain. 



I. Environmental causes. (Merely a few examples will be 

 indicated. This part of the subject properly belongs to the 

 ecologist and physiologist.) 



The examples of environmental causes given below commonly 

 result in complete sterility A, although under special circumstances 

 situations corresponding to B or C might be set up. 



I. Conditions too moist. 



When species that have become adapted to relatively dry 

 conditions are subjected, at the lime pollen is mature and shedding, 

 to unusually moist conditions, the pollen grains may absorb 

 enough moisture to swell up and burst prematurely, thus losing 

 their usefulness. (The sex act might also be circumvented by 

 hard rain coming immediately after pollen distribution, which 



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