182 PLANT DISTRIBTTTION. 



plants whicli frequent cultivated lands, or whicli follow tlie 

 movements of man, such as the annual poa grass, the shepherd's 

 purse, the common fumitory, and the chickweed.* 



It would seem, then, from what has been stated, that the 

 wanderings of perennials have been, and still are, more wide- 

 spread than those of annuals, and that, given a centre in which 

 both occur, the former will eventually stamp out many of the 

 latter, and spread further afield. Dean Herbert put the question 

 in a nutshell when he said " plants do not grow where they like 

 best, but where other plants will let them." 



To dogmatize or even theorize from these data were 

 a decidedly unscientific method of treating a very scientific 

 subject ; but, obviously enough, we have here a subject the study 

 of which may clear many difficulties now surrounding the present 

 distribution of plants. 



* That man is responsible for the wanderings of many annuals into remote 

 countries, is clearly proved by the experience of Sir J. D. Hooker, in the 

 Himalayas — ^" Along the narrow path I found the two commonest of all British 

 weeds, a grass fPoa annua), and the Shepherd's purse ! They had evidently been 

 imported by man and yaks, and as they do not occur in India, I could not but 

 regard these little wanderers with the deepest interest. Such incidents as these 



give rise to trains of reflections in the mind of the naturalist traveller 



At this moment these common weeds more vividly recall to me that wild scene 

 than does all my Journal, and remind me how I went on my way, taxing my 

 memory for all it ever knew of the geographical distribution of the Shepherd's 

 purse, and musing on the probability of the plant having found its way thither 

 over all Central Asia, and the ages that may have been occupied in its march." — 

 Himalayan Journals, Chap. ix. 



