20 ANNALS NEW YORK ACADEMY OF SCIENCES 



nine chromosomes to certain spores. Here evidently there is less irregu- 

 larity than in Karpechenko's material. 



In most studies of irregularities in sporogenesis attention has heen 

 directed chiefly to the irregular distribution that accompanies the pres- 

 ence of unpaired chromosomes. A double splitting with partial or in- 

 complete separation such as is seen in the Europa clon may be more 

 general than is now apparent. 



Types of Sterility Involving Abortion of Spores 



It is to be recognized that there are several types of germ-cell abor- 

 tion in flowering plants, especially in respect to that condition or status 

 of the plant which may, perhaps, be regarded as an underlying or funda- 

 mental cause of the sterility. On this basis the following classes of 

 sterility due to spore abortion may be recognized : — 



1. Abortion of sporophylls, of spores and of sex cells is a character- 

 istic feature of inter sexualism. In extreme cases of male sterility in 

 intersexes the stamens are merely rudimentary organs, as in Plantago 

 lanceolata (Stout, 1919). In certain other pollen-sterile plants, such 

 as the Brighton grape (Dorsey, 1914), the abortion occurs after the for- 

 mation of pollen grains by a degeneration of the generative cell or of 

 the divisions that produce that cell. In such extreme cases of cyclic 

 alternations in sex as are seen in Cleome spinosa (Stout, 1923) there is an 

 alternating graded series of abortions in the development of the flowers 

 throughout the flowering period. At one time the pistils are aborted 

 and at another time the stamens are aborted, and in the climax the 

 abortion of sporophylls reduces them to merely rudimentary structures. 



The distinguishing feature in the intersexes is that the abortion is 

 typically merely one-sided. There is an abortion of one sex while the 

 other may be fully functional. In intersexes the abortion is obviously. 

 not due fundamentally to misfits in the relations of chromatin material 

 or to the erratic behavior of chromosomes but to a loss of maleness or 

 of femaleness through some fundamental systemic regulation that is 

 regularly hereditary. Both as to expression and cause it is distinct from 

 various other types of sterility which involve abortion of sex organs. 



It is clear thai the abortion of spores as developed in the Europa 

 don is not that of intersexes, for it obviously affects both microspores 



and [microspores to the same degree and at the same time. 



2. Cytological studies of the pollen sterility of hybrids have been 

 numerous since such earlier studies as those of duel ( L900) for Syringa 



