BULBILS AND GEMM^. 125 



same author remarks : — "G-rowth is only an excess of nutrition, 

 and generation is only an excess of growth. Growth and gener- 

 ation have for cause a superabundance of nutritive materials."* 



Among cryptogams the situation is analogous. The funda- 

 mental rule is, — many spores few gemmee ; many gemmae few 

 spores. Take the mosses. Antheridia and Archegonia, the 

 functional equivalents of the stamens and pistils of flowering 

 plants, are the prevailing mechanism by which these lowly types 

 of plant life perpetuate themselves, but, like the stamens and 

 pistils of flowering plants, they are not invariably responsible 

 for reproduction. 



Aulacomnium palustre, which keeps company with the sphag- 

 num mosses on our moorlands, in some seasons develop spores by 

 the usual sexual process, while at other seasons spores are left 

 severely out of the question, their purpose being fully met by 

 gemmse, which are borne on stalks at the extremities of the 

 branches. Lord Justice Fry, himself a very capable muscologist, 

 says — "The question whether the plant shall adopt the one mode 

 of reproduction, or the other, seems to depend, in part at least, on 

 temperature, a high temperature tending towards the production 

 of the gemmae, and a lower temperature towards spores, "f 



Orthotrichum phyllanthum, another moss which is tolerably 

 cosmopolitan in its distribution, favours the vegetative method 

 of reproduction to a still more marked degree. Once or twice 

 only has it been found bearing spores, while of gemmae it 

 produces large numbers at the apices of the leaves. 



Leptodontium, Grimmia, Tortula, Bryum and TetrapJiis, are 

 other mosses which, either on the midrib, at the apices, or in the 

 axils of the leaves, and in terminal cups bear gemmae, and on 

 which spores are only occasionally found. 



Proceeding to still lower types of vegetation, the relation of 

 gemmae to the sexual modes of reproduction becomes strikingly 

 exemplified in the frondose liverworts. Repeatedly has the 

 writer noticed that some years are years of gemmae, while others 

 are years of sexual organs. The two, in short, are never borne 

 in large numbers on one plant at the same time. One kind, 



* Ibid, p. 309. 



t British Mosses, Knowledge Series, pp. 23, 24. 



