SEASIDE WEEDS. 163 



set it down as a desert species at once. 

 Indeed, so naturally do all these peculiari- 

 ties result from the mode of life affected by 

 sand-haunting plants, that in India, where 

 there are no true cactuses, certain native 

 spurges are universally known by that name, 

 because they so exactly resemble them in 

 general external appearance. By pedigree 

 the two families are wholly unconnected; 

 but in America certain weeds of a kind some- 

 thing like our own stone-crops and house- 

 leeks, having got loose on the sand-wastes 

 of the. tropical belt, adapted themselves by 

 their succulence and their defensive prickles 

 to the necessities of their new situation, while 

 in Asia certain totally distinct weeds of a 

 kind closely resembling our spurges and 

 mercuries happened to establish themselves 

 on the similar sand-wastes of sub-tropical 

 India, and necessarily adapted themselves in 

 just the same manner to just the same sort 

 of situations. 



In fact, we now know that these adaptive 



M 2 



