668 LECTURE XXIII. 



a difference in reaction between the generative and the vege- 

 tative nucleus ; that the former, namely, stains more deeply 

 than the latter, a reaction which indicates the presence of a 

 larger proportion of nutritive hyaloplasm in the former. If 

 this be so, then, conversely, the proportion of nucleo-idioplasm 

 in the vegetative nucleus is greater than in the generative 

 nucleus. It is not possible to press this fact closely, for 

 it is not clear that Weismann's "reproductive substance" 

 corresponds exactly to Strasburger's nucleo-idioplasm, and 

 Weismann says nothing about the staining properties of the 

 "reproductive substance"; but as far as it goes it seems 

 to shew that the vegetative nucleus not only contains some 

 nucleo-idioplasm or "reproductive substance," but that it 

 actually contains more than the generative nucleus. 



The conclusions, as to the physiological significance of 

 the extrusion of the polar body, to be drawn from the fore- 

 going discussion are the following. It appears, in the first 

 place, in view of the parthenogenesis of the Saprolegnieae, 

 the only case of parthenogenesis, be it said, which has been 

 thoroughly investigated, that the extrusion, in some form, 

 of a polar body is an essential part of the development of 

 a gamete. We cannot, therefore, agree with Strasburger's 

 views on the subject (see p. 659). It is true that the ex- 

 trusion of a polar body has not been observed in the case of 

 all plants, but the observations on the subject are not 

 so numerous or extended as to warrant the inference that 

 the process does not take place in all. In the second place, 

 in view of the fact that the essential feature of the sexual 

 process is the coalescence of the nuclei of the two gametes, 

 we cannot but conclude that the extrusion of the polar body 

 involves in all cases the extrusion of a portion of nuclear 

 substance. Here again we are at issue with Strasburger. 

 Thirdly, we conclude that Weismann's view as to the nature 

 of the substance of the polar body is not established : what 

 facts there are go to prove that the nucleus of the polar 

 body consists not of histogenic nucleo-plasm, but of nucleo- 

 idioplasm. Finally, we conclude that it is this reduction of 

 its nucleo-idioplasm which determines the sexuality of the 



