AUGUST WEISMANN 345 



to flowers, fruit and seeds, from which new plants arise. "It is easy 

 to grow new plants from the leaves of begonia which have been cut 

 off and merely laid upon moist sand, and yet in the normal course of 

 ontogeny the molecules of germ-plasm would not have been compelled 

 to pass through the leaf ; anci they ought therefore to be absent from 

 its tissue. Since it is possible to raise from the leaf a plant which 

 produces flower and fruit, it is perfectly certain that special cells con- 

 taining the germ-substance cannot exist in the plant." But I think 

 that this fact only proves that in begonia and similar plants all the 

 cells of the leaves or perhaps only certain cells contain a small amount 

 of germ-plasm, and that consequently these plants are specially adapted 

 for propagation by leaves. How is it then that all plants cannot be 

 reproduced in this way ? No one has ever grown a tree from 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 admix- 

 ture of a minute quantity of unchanged germ-plasm with some of their 

 nuclei. 



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

 page 'J2'>^ — "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 

 ^gg 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 



