PBESIDENTIAL ADDRESS — SECTION D. 177 



Moreover, the situation of this germ- plasma in relation to 

 other protoplasmic elements of the organism is a special one. 

 The germ-plasma is not capable of being influenced or affected 

 by neighbouring cells except as regards its nutrition. It re- 

 tains an altogether isolated position, and, however parts of the 

 organism might become modified in the course of the life of 

 the individual, the germ-plasma would be in no way altered. 



It follows, as a necessary deduction from these two posi- 

 tions, that the germ-plasma is continuous, and that it is 

 completely isolated,- — that acquired characters cannot be trans- 

 mitted. 



But the isolation and continuity of the germ-plasma seem 

 to be at variance with a good many well-known facts ; and in 

 the attempts which in some cases Weismann has made to re- 

 concile these facts with his theory, or to modify, as seemed 

 sometimes necessary, the theory to accord with the facts, all 

 that is distinctive iu these doctrines of his becomes completely 

 lost. 



The whole vegetable kingdom abounds with facts that 

 cannot be reconciled with this view ; but the case of certain of 

 the higher plants affords perhaps the most cogent and conclu- 

 sive evidence. In ordinary higher plants the germ-plasmata 

 must be contained, not merely potentially but actually, in the 

 meristem of the growing-point ; and it might thus be traced 

 back from its final situation in the matui'e pollen-grain or 

 embryo-sac to the germ-plasm of the parent oosphere. It 

 seems difficult to understand how this could take place. The 

 continuous division and differentiation of the cells of the 

 meristem ; the discontinuous mode of development of the germ- 

 plasmata, its cessation during long intervals of active vegeta- 

 tive reproduction ; and its renewal, the occurrence of which is 

 capable of being determined in many cases by extraneous con- 

 ditions — all these circumstances make it very diflicult to believe 

 in the isolation and continuity of the germ-plasm. Still, it is 

 at least conceivable that in some way or other there is isola- 

 tion and continuity. But when we come to consider the case 

 of certain of the higher plants, such as the Begonias, in which 

 a complete plant with male and female germ-plasmata may be 

 developed from a leaf or a bit of a stem, it is impossible longer 

 to admit Weismann's two fundamental positions. Then there 

 is no growing-point with imperfectly differentiated cells, and a 

 new growing-point or -points has to be formed from the cam- 

 bium-cells present in the vascular bundles of the leaf; and, if 

 these contain germ-plasma, then the latter must be distributed 

 in the cambium-cells throughout the whole plant. 



The series of phenomena here referred to were specially 

 adverted to by Strasburger when criticizing Weismann's 

 theory as it originally appeared ; and iu the English version 

 12 



