GENERAL OBSERVATIONS AND CONCLUSIONS. 459 



In other terms, in such cases they do not pass out of the 

 condition of adventitious plants. 



3. It cannot be supposed that they are derived within 

 historic times from certain allied species. 



These three characters are found united in the follow- 

 ing species : — Bean (Faha vulgaris), chick-pea {Cicer 

 arietiniiin), ervilla {Ervmn Ervilia), lentil (Ervum lens), 

 tobacco {JSHcotiana tabacum), wheat (Triticum vul- 

 gare), maize {Zea mays). The sweet potato {Convol- 

 vulus batatas) should be added if the kindred species 

 were better known to be distinct, and the carthamine 

 (Carthanius tinctorius) if the interior of Arabia had been 

 explored, and we had not found a mention of the plant 

 in an Arabian author. 



All these species, and probably others of little-known 

 countries or genera, appear to be extinct or on their way 

 to become so. Supposing they ceased to be cultivated, 

 they would disappear, whereas the majority of culti- 

 vated plants have become somewhere naturalized, and 

 would persist in a wild state. 



The seven species mentioned just now, excepting 

 tobacco, have seeds full of fecula, which are the food of 

 birds, rodents, and different insects, and have not the 

 power of passing entire through their alimentary canal. 

 This is probably the sole or principal cause of their 

 inferiority in the struggle for existence. 



Thus my researches into cultivated plants show that 

 certain species are extinct or becoming extinct since the 

 historical epoch, and that not in small islands but on 

 vast continents without any great modifications of 

 climate. This is an important result for the history of 

 all organic beings in all epochs. 



Article V. — Concluding Remarks. 



1. Cultivated plants do not belong to any particular 

 category, for they belong to fifty- one difierent families. 

 They are, however, all phanerogamous except the mush- 

 room (Agaricus cam'pestris). 



