Partial Variability and Vegetative Propagation. 145 



half took on the famihar dwarf habit of alpine plants 

 while the latter soon exhibited the general features of 

 lowland plants. The leaves of alpine plants are smaller, 

 thicker, firmer and more compact in build, poorer in air 

 spaces, richer in chlorophyll and dark green; in a given 

 period of time they assimilate more carbonic acid gas 

 than the corresponding parts of plants grown in the plain. 

 They are perfectly adapted to the bright light and the 

 short summer of the Alps ; in the space of a few weeks 

 they have to store up nourishment for the wdiole year. 

 The underground stem of an alpine plant is well devel- 

 oped and richly branched ; the exposed parts are on the 

 other hand short and consist of few and stunted inter- 

 nodes; it has large flowers and so forth. In all these re- 

 spects the half -specimens transplanted to the Alps as- 

 sumed the characters of normal alpine plants. 



Arctic plants exhibit a corresponding adaptation ; the 

 climate is of course cold, but the air is damp, and this 

 affects the anatomical structure of the leaves. This case 

 of partial variability has also been investigated by Bon- 

 nier, and with analogous results. 



I have carried out similar experiments, on a Crassula- 

 like composite Othonna crassifolia^ It is a South Afri- 

 can plant with almost cylindrical fleshy leaves pointed at 

 the end. The development of these leaves is to a great 

 extent dependent on the dampness of the air and the 

 ground. Grown in damp soil, the Othonna is dark green, 

 with long leaves, it is richly branched and of very luxuri- 

 ant growth; grown in dry soil on the other hand it is 

 very pale green, with short globose leaves, and hardly 

 branched at all. They also exhibit a dependence on ex- 

 ternal conditions in the number of their ray-florets, a 



^ Kruidk. Jaarbock Dodonaea. Bd. XII, 1900, Taf. i. 



