314 COLLECTION AND ARRANGEMENT OF PLANTS. 



place, to collect Plants from all sources open to him ; and he then 

 arranges them according to their species. Thus, we will sup- 

 pose that he has collected all the plants of Great Britain, and 

 that he has obtained a corresponding series of the plants of France. 

 Upon bringing them together, he would find that many species 

 are common to the two countries ; but that some are peculiar to 

 Britain, others to France. If he obtained, in addition, a col- 

 lection of Spanish plants, he would find that some of the species 

 common to Britain and France are contained in it also ; and 

 that some species not known in Britain are common to France 

 and Spain ; but he will find many peculiar to Spain. Proceed- 

 ing thus orer the whole world, he would gradually increase his 

 number of new species ; at the same time adding considerably to 

 the number of specimens of some which he would find very ex- 

 tensively diffused. He would find a few similar species almost 

 everywhere, these being the kinds most capable of adapting 

 themselves to varieties in soil, climate, &c. ; whilst, on the other 

 hand, he would find many of a very limited distribution, being 

 restricted to some small extent of country, in which alone they 

 can find the conditions necessary for their growth. 



475. The greatest difficulty in this part of the investigation 

 consists in the discrimination of species really distinct, that is to 

 say, of races which have maintained their distinctive peculiarities, 

 so constantly, that they must be considered as having had ori- 

 ginally different stocks, from those varieties (. 16), which may 

 often present differences really greater in amount than those 

 which exist between many undoubtedly distinct species, but 

 which all sprung from the same original stock. Thus, for ex- 

 ample, a collection of plants from different parts of India would 

 contain many specimens presenting such marked differences, 

 that the inexperienced Botanist would not hesitate to set them 

 down as distinct species ; yet to one who has carefully examined 

 the subject, and has made himself acquainted with the variations 

 produced by the differences in soil and climate so striking in 

 this extensive tract, it becomes apparent that they are all mem- 

 bers of the same. There is, too, in many species a remarkable 

 tendency to run into spontaneous variations, for which no exter- 



