2l6 THE GERM-PLAS^r 



be formed anew. In answer to this it might be urged that the 

 somatic cells of ferns have become too highly differentiated : but 

 this is contradicted by the fact that many, although by no 

 means all, ferns can produce bulbils on their fronds. I must 

 leave botanists to decide why this occurs ; but were I asked 

 ■whether the power of producing entire plants from somatic cells 

 would not have been of advantage to the other ferns, and would 

 therefore be expected to be possessed by them. I should be in- 

 clined to reply that all ferns are able to replace lost fronds by 

 forming new ones, — not by the regeneration of the injured leaf, 

 but by budding from the stem. This suffices to restore the plant 

 when it has been injured. 



We must now consider the Phanerogams in this connection. 

 In these plants, again, 'accessor}' germ-tracks ' are usually absent 

 in the leaves : that is to say, the cells of the leaves are not 

 capable of producing buds or even of restoring a piece which has 

 been cut out The axes of the shoots, on the other hand, possess 

 this power in a high degree, and it depends on the presence of 

 cambium cells, all of which are apparently capable of giving rise 

 to new growing points, which produce new shoots with leaves 

 and blossoms, and consequently also germ-cells. The power of 

 regenerating tJte leaves is, as a rule, useless ; for the formation 

 of new persons of the plant stock can take place to an unlimited 

 extent by means of the cavibial layer : and this mode of compen- 

 sation for losses sustained is more effectual than the restoration 

 of defects in the leaves would be. The power of growing adven- 

 titious buds is probably unnecessary in the case of most leaves, 

 on account of the enormous number and certain dispersion of 

 the seeds produced by the plant. Amongst animals the same is 

 true as regards polype-stocks. Cells are distributed through- 

 out the stock which have the appearance and functions of 

 ordinary somatic cells, but which can give rise to new persons 

 under certain circumstances, such as, for instance, when the 

 stock has become injured. In a living stock of Tubitlaria 

 mesembryanthemum, which I once brought from Marseilles to 

 Freiburg, the crowns of the polvpe died one after the other 

 within a week, probably on account of want of nourishment ; 

 but within a few days afterwards all the stalks had given rise to 

 new crowns ; and though these were very small, they would un- 

 doubtedly have grown to the full size had it been possible to sup- 

 ply them with food. The capacity for regeneration is apparently 



