CH. II] THE PODOSTEMACEAE 9 



larger to well-marked varieties, to species, and to higher forms. 

 There is no inherent reason why economic botany should remain 

 what it now is, an ever-increasing mass of facts with little or no 

 co-ordination. What little of this there is, as may be seen at once 

 by consulting Wiesner's standard treatise, is very largely 

 confined to such observations as that a and h, belonging to the 

 same family, produce similar economic products. This alone 

 shows that the facts of economic botany must be explicable upon 

 evolutionary lines. Yet, with the exception of the theory that 

 poisonous plants have evolved the poison as a protection against 

 animals, natural selection has never attempted to explain any- 

 thing in the realm of economic botany, which ought by this time 

 to be a properly classified scientific discipline, with general 

 principles running through it. One chemical fact must follow 

 from another. 



Something the same may be said of geographical distribution, 

 which has been a favourite study of the author for the last thirty- 

 five years. This again consists of a stupendous mass of facts, 

 connected together by little more than a tissue of speculation. 

 Sir Joseph Hooker, its great leader of former days, wrote: "All 

 seem to dread the making Botanical Geography too exact a 

 science; they find it far easier to speculate than to employ the 

 inductive process", and the position is not so very different 

 even yet. It has always been admitted that any theory of the 

 mechanism of evolution must stand or fall according to whether 

 it can or cannot interpret the facts of distribution. The two are 

 obviously and inextricably bound together and to them should 

 be added the facts of economic botany. 



At first natural selection seemed to offer an explanation of 

 these geographical facts, indeed so promising an explanation 

 that Hooker became one of Darwin's chief lieutenants, never 

 following out to their conclusions some of the lines of work upon 

 which he had begun. Gradually, however, it was discovered 

 that the employment of natural selection was not leading to real 

 advance, and the first enthusiasm died away, leaving distribution 

 in the Cinderella-like position that it still occupies. Those who 

 had leanings in the direction of distributional study turned more 

 and more to the rising science of ecology, known as natural history 

 of plants when the author taught the beginnings of it under Sir 

 Francis Darwin in 1891-4. But though ecology is all-important 

 for the details of local distribution, it cannot answer the wide 

 questions which are the province of geographical distribution 



