THEIR SIGNIFICANCE IN HEREDITY. 377 



expression of a mature opinion. From the very numerous and 

 mostly minute and careful observations which have been hitherto 

 recorded, we cannot conclude with any degree of certainty when 

 and how the ' reducing division ' of the nucleus takes place, nor can 

 we decide upon the processes which signify the purification of the 

 germ-plasm from the merely histogenetic part of the nucleoplasm. 

 But perhaps it has not been without value as regards future in- 

 vestigation that I have tried to apply to the male germ-cells the 

 views gained from our more certain knowledge of the corresponding 

 structures in the female, and thus to indicate the problems which 

 now chiefly demand solution. 



IV. THE FOREGOING CONSIDERATIONS APPLIED TO PLANTS. 



It remains to briefly consider the case of plants. Obviously, the 

 'reducing division' of the germ-nuclei, if it takes place at all, 

 cannot be restricted to the germ-cells of animals. There must 

 be a corresponding process in plants, for sexual reproduction is 

 essentially the same in both kingdoms ; and if fertilization must 

 be preceded by the expulsion of half the number of ancestral germ- 

 plasms from the eggs of animals, the same necessity must hold 

 in the case of plants. 



But whether the process always takes place in the form of polar 

 bodies, and not perhaps principally, or at any rate frequently, in 

 the form of equal cell-division, is another question. It is true that 

 polar bodies occur in numerous plants, as we chiefly know from 

 Strasburger's researches 1 . Strasburger shows that cells are se- 

 parated by division from the germ-cells, and perish. But it seems 

 to me doubtful whether we must always regard their formation as 

 the removal of half the number of ancestral germ-plasms rather 

 than the histogenetic nucleoplasm of the germ-cell. It appears to 

 me that histogenetic nucleoplasm must be present in the highly 

 differentiated vegetable germ-cells, especially in the male cells, and 

 also that it must be removed during the maturation of the cell, if 

 my idea of the histogenetic nucleoplasm be accepted. It is very 

 possible, as I have already mentioned, that there may be quite 

 indifferent germ-cells, viz. cells which are entirely without specific 

 histological structure, and in such cases histogenetic nucleoplasm 



1 1. c., p. 92. 



