44 THE WATER-BALANCE OP SUCCULENT PLANTS. 



As regards mode of growth, the case of the bisnaga is instructive. Its 

 form, at first nearly spherical, becomes, later, irregularly columnar, and 

 it then simulates the habits of the sahuaro, but its root, apparently quite 

 insiifficient for the support and anchorage of a heavy column, is often torn 

 from its place as the unwieldy trunk is prostrated by desert winds or over- 

 turned by its own weight. The apical growth of this plant, however, is 

 unsymmetrical and extremely slow; facts that, coupled with the frequent 

 destruction of the bisnaga in the manner indicated, suggest a relatively ill - 

 adapted form, a view which receives confirmation from the sparse occur- 

 rence of this plant in regions where it is now found. These, however, are 

 speculative considerations which may well be deferred to a period of greater 

 knowledge. 



In general, it may be said that whatever may be the theoretical interest 

 established by the series of observations and measurements now brought to a 

 close, it is quite possible that their chief value lies in the close approach to a 

 quantitative expression of certain biological relations, carried out through 

 a period of years. The determination of such relations by weighing and 

 measuring, though possible at present only in a relatively limited field, is to 

 be regarded as a step towards the exactness of conception and expression 

 which should be realized in the further development of biological science. 



