,8,,. DR. WEISMANN'S THEORY OF HEREDITY. 173 



formed. This conclusion is based upon the fact that germ-cells only 

 occur in certain localised areas " (p. 207). 



Dr. Weismann now endeavours to apply his hypothesis of germ- 

 plasm being limited to a certain series of somatic cells to plants. 

 Since, however, Begonias can be propagated by their leaves, he 

 admits : — " 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" (p. 211). 

 He then proceeds to base an argument upon this, as follows : — "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." The author here 

 infers that because no one has raised tulips from their leaves, there- 

 fore it cannot be done ! The fact, of course, really is that it has 

 never been worth while to do it. If, however, a premium were 

 offered for tulips or oak trees raised from leaf-cuttings, plenty would 

 soon be forthcoming. It is known to all horticulturists and 

 botanists that there is virtually no limit to the propagation by leaves 

 or any other part of a plant. ^ The sole conditions are the presence of 

 " embryonic " cells, and a sufficient amount of nutritive material at 

 the section to enable the part to develop roots. 



Reading in Sachs' lectures on the Physiology of Plants, + that 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, Dr. Weismann makes the further admission : 

 " We have here a case which requires the assumption that all or nearly 

 all cells must contain germ-plasm " (p. 212). He does not seem aware 

 that the propagation by roots, stems, leaves is habitually practised 

 in all kinds of plants whenever desirable, that the power of hereditary 

 reproduction by the vegetative system is no special peculiarity of 

 Begonias and Mosses, but a universal feature of the vegetable 

 kingdom. Even fruits such as cucumbers, prickly pears, and 

 strawberries have been known to send out roots and buds. 



This fact is, of course, perfectly well-known to all botanists and 

 horticulturists, and needs no further illustrations. Dr. Weismann's 

 mistake lies, therefore, in supposing the phenomenon to be 

 exceptional instead of general. 



Moreover, besides the production of flowers, fruits, and seeds 

 from the vegetative system, it must be remembered that roots, usually 

 confined to subterranean regions, can be produced anywhere in the 



^ For example, though it is usual to propagate Chrysanthemums by stem- 

 cuttings, a florist exhibited at one of the exhibitions of the Royal Horticultural 

 Society a large quantity raised from leave's. The Dutch propagate Hyacinths solely 

 rom sections of leaf-scales, &c.' 



* P. 723, English Edition. 



