154 Mr Gregory, The Abortive Development 



Such evidence as is obtainable, both from experimental breeding, 

 and more particularly from cytological work, points to the reduction 

 division as the time at which the segregation of allelomorphic 

 characters takes place. It is therefore interesting to notice that, 

 in the sterile Sweet-Peas, abnormalities appear during the processes 

 preparatory to this division, and only then. 



The exact bearing of this observation upon our theories of 

 the individuality of chromosomes, and their importance in the 

 transmission of segregated characters, is, however, not very 

 clear. 



Sterility, in the case with which we are dealing, is a recessive 

 character, and is almost always confined to those plants which 

 have light-coloured leaf axils — another recessive character. No 

 segregation of the characters in question is therefore taking place 

 at the formation of the gametes. The irregularities do not there- 

 fore correspond with defective segregation. 



Further, it must be noticed that the irregularity affects the 

 whole nucleus and is not confined to any particular pair of chromo- 

 somes. Although this may simply imply — what recent cytological 

 work has led us to expect — that individual chromosomes may 

 influence the behaviour of their fellows, it seems more likely that 

 sterility of the male organs is the expression of some deeper-lying 

 phenomenon affecting the physiology of the whole plant. It is 

 moreover almost always coupled with another physiological 

 character — the absence of colour from the leaf axils even in 

 plants with coloured flowers* 



In further support of this view we have the most important 

 fact that the nucleus of the embryo-sac mother-cell, which pos- 

 sesses a series of chromosomes exactly homologous with those of 

 the pollen-mother-cells, shows no abnormality whatever. 



The low staining capacity of many of the abnormal nuclei (see 

 p. 152) might indicate a low state of nutrition, although there is 

 no obvious difference between the development of the vascular 

 strands in the fertile and sterile stamens. Possibly a similar 

 deduction may be drawn from the fact that the development of 

 spindle fibres in the cytoplasm is feeble or absent. 



If this view be correct, it may be that the sterility of the male 

 organs in these Sweet-Peas is not fundamentally different from 

 that which has been observed, also in the male organs only, in 

 a certain family of Primula Sinensis. There is some indication 

 that the contabescence of the anthers in this latter case is an 

 inherited (recessive) character. In these plants the degree of 

 contabescence varies with each anther, and a small amount of 

 good pollen is produced. 



* See also Bateson, Saunders, and Punnett, I.e., pp. 91, 92, on the existence of 

 two classes among the white-flowered plants. 



