658 LECTURE XXIII. 



advance made in one generation, the nature of the advance 

 being determined largely by the external conditions. With 

 regard to reversion, he assumes that newly acquired properties 

 of the idioplasm may remain latent, and thus the older 

 properties of the idioplasm will be able to assert themselves. 



It is impossible, within our present limits, to enter into 

 the detail of Naegeli's theory of the constitution of the idio- 

 plasm, and it is therefore also impossible to minutely criticise 

 it. The distinction of an active protoplasm, the idioplasm, 

 in the organism is certainly an assistance to our apprehension 

 of physiological facts; it leads us to regard the protoplasm 

 of the plant-body as constituting a whole. And, like the 

 theory of pangenesis, it enables us to obtain an insight into 

 the facts of reproduction, with this advantage, that it is not so 

 inherently improbable. 



We come now to Strasburger's theory of reproduction. 

 He agrees with Naegeli in the opinion that the active pro- 

 perties of protoplasm reside in a particular portion of it. 

 He distinguishes, alike in the nucleoplasm and in the cyto- 

 plasm, a nutritive hyaloplasm and a formative hyaloplasm, 

 the latter corresponding to Naegeli's idioplasm; the nucleo- 

 hyaloplasm constitutes a single coiled filament (see p. 27), 

 whereas the cyto-hyaloplasm has no constant arrangement. 

 But Strasburger differs from Naegeli in that he attributes a 

 functional predominance to the nucleo-idioplasm. So long 

 as a cell is capable of growth, it is the nucleus which deter- 

 mines the growth and the mode of growth. The metabolism 

 of the nutritive cytoplasm is directed by the nucleus so that 

 the products are of a particular kind and nourish the idioplasm 

 in a particular manner. Thus, in a germinating spore, the 

 formative activity of the cyto-idioplasm is controlled so that 

 the characteristic form of the developing organism is grad- 

 ually evolved. Strasburger agrees with Naegeli that the 

 reproductive capacity of a cell depends upon its being in 

 the embryonic condition, and points out that the character- 

 istic feature of this condition is the enormous size of the 

 nucleus in relation to the cytoplasm. From this point of 

 view the great capacity of plants for vegetative reproduction 



