212 THE CONTINUITY OF THE GERM-PLASM AS THE 



the leaf of the lime or oak, or a flowering plant from the leaf 

 of the tulip or convolvulus. It is insufficient to reply that, in the 

 last-mentioned cases, the leaves are more strongly specialized, and 

 have thus become unable to produce germ-substance ; for the leaf- 

 cells in these different plants have hardly undergone histological 

 differentiation in different degrees. If, notwithstanding, the one 

 can produce a flowering plant, while the others have not this 

 power, it is of course clear that reasons other than the degree 

 of histological differentiation must exist ; and, according to my 

 opinion, such a reason is to be found in the admixture of a minute 

 quantity of unchanged germ-plasm with some of their nuclei. 



In Sachs' excellent lectures on the physiology of plants, we read 

 on page 7 23 l ' In the true mosses almost any cell of the roots, 

 leaves and shoot-axes, and even of the immature sporogonium, 

 may grow out under favourable conditions, become rooted, form 

 new shoots, and give rise to an independent living plant.' Since 

 such plants produce germ-cells at a later period, we have here 

 a case which requires the assumption that all or nearly all cells 

 must contain germ-plasm. 



The theory of the continuity of the germ-plasm seems to me 

 to be still less disproved or even rendered improbable by the facts 

 of the alternation of generations. If the germ-plasm may pass on 

 from the egg into certain somatic cells of an individual, and if it 

 can be further transmitted along certain lines, there is no difficulty 

 in supposing that it may be transmitted through a second, third, 

 or through any number of individuals produced from the former by 

 budding. In fact, in the Hydroids, on which my theory of the 

 continuity of the germ-plasm has been chiefly based, alternation 

 of generations is the most important means of propagation. 



II. THE SIGNIFICANCE OF THE POLAR BODIES. 



We have already seen that the specific nature of a cell depends 

 upon the molecular structure of its nucleus ; and it follows from 

 this conclusion that my theory is further, and as I believe strongly, 

 supported, by the phenomenon of the expulsion of polar bodies, 

 which has remained inexplicable for so long a time. 



1 English translation, by H. Marshall Ward. Oxford, 1887, Clarendon Press. 



