454 Ever-sporting Varieties 



DimorpMsm is of universal occurrence in tiie 

 whole vegetable kingdom. In some cases it is 

 typical, and may easily be discerned from ex- 

 treme flutuating variability. In others the con- 

 trast is not at all obvious, and a closer 

 investigation is needed to decide between the 

 two possibilities. Sometimes the adaptive qual- 

 ity is evident, in other cases it is not. A large 

 number of plants bear two kinds of leaves linked 

 with one another by intermediate forms. Often 

 the first leaves of a shoot, or those of accident- 

 ally strong shoots, exhibit deviating shapes, 

 and the usefulness of such occurrences seems to 

 be quite doubtful. The elongation of stems and 

 linear leaves, and the reduction of lateral or- 

 gans in darkness, is manifestly an adaptation. 

 Many plants have stolons with double adapta- 

 tions which enable them to retain their char- 

 acter of underground stems with bracts or to 

 exchange it for the characteristics of erect 

 stems with green leaves according to the outer 

 circumstances. In some shrubs and trees the 

 capacity of a number of buds to produce either 

 flowers or shoots with leaves seems to be in 

 the same condition. The capacity of producing 

 spines is also a double adaptation, active on 

 dry and arid soil and latent in a moist climate 

 or under cultivation, as with the wild and cul- 

 tivated apple, and in the experiments of Lo- 



