PBESIDENTIAL ADDRESS — SECTION D. 179 



111 some instances, then, when two nearly-related species 

 aie grafted together there are produced flowers, and eventually 

 fruits, which partake in some degree of the characters of both 

 species. Here, germ-plasma, if we are to accept Weismann's 

 view, still remaining isolated, must have travelled up from the 

 cells of the cambium of the lower stock through the cambium- 

 layer of the graft to the growing-point to take part in the 

 formation of the germ-plasmata of the hybrid flowers. In the 

 lower plants this wide distribution of germinal matter reaches 

 a still higher limit. The whole plant in some cases can be 

 pounded up into minute fragments, each of which is capable of 

 giving rise to a fresh plant, and thus of developing new germ- 

 plasmata ; so that germ-plasm in such cases must be present 

 in all the ordinary cells of the plant. But how can we assert 

 of a substance which is contained in the protoplasm of all the 

 cells of a plant, or of all the cells of the actively-growing 

 tissues, that it is kept apart from the rest of the organism, and 

 is therefore not liable to be influenced by conditions ailecting 

 the ordinary cells ? 



There is, in fact, absolutely no evidence of the existence 

 ■of a special germ-plasma handed down in all cases from 

 generation to generation : on the contrary, the germ-plasma 

 may be, and is in a great number of cases, derived not from 

 a special antecedent germ-plasm, but from the contents of 

 somatic cells sometimes displaying a high degree of histological 

 differentiation. 



These phenomena of vegetable physiology seem to me to 

 impress on us the conclusion that, in spite of the complexity 

 of structure which it exhibits, all the parts of the higher plant 

 are in close vital continuity, so that no group of its cells is 

 capable of remaining uninfluenced .by the condition of the 

 rest. 



It is from the vegetable kingdom that we get the strongest 

 evidence against the theory of the continuity of the germ- 

 plasma ; but from the animal side there is nothing that can be 

 construed into evidence that a general law of this kind obtains, 

 while, on the other hand, there is a great deal that tends to 

 corroborate and confirm the conclusion to which we are led by 

 the study of the development of plants. True, there are cases 

 in the animal kingdom in which such a continuity actually 

 occurs ; there are cases in which, at an earlier or later stage in 

 embryonic life, there are separated off cells which are destined 

 to give origin only to the reproductive elements, and which 

 take no share in the formation of other tissues of the body. 

 But at the other extreme are cases in which the sexual 

 elements make their appearance at a late period in the life- 

 history of the animal, and may be developed from cells which 

 for a considerable time have remained undistinguishablc : and 



