GENERAL OBSERVATIONS AND CONCLUSIONS. 453 



When a species has been once cultivated, it is rarely, i 

 perhaps never completely, abandoned. It continues to' 

 be here and there cultivated in backward countries, or' 

 those whose climate is especially favourable. I have 

 passed over some of these species which are nearly 

 abandoned, such as dyer's woad (Isatis tinctoria), mallow 

 {Malva sylvestris), a vegetable used by the Romans, and 

 certain medicinal plants formerly much used, such as 

 fennel, cummin, etc., but it is certain that they are still 

 grown in some places. 



The competition of species causes the cultivation of 

 some to diminish, of others to increase ; besides, vegetable 

 dyes and medicinal plants are rivalled by the discoveries 

 of chemists. Woad, madder, indigo, mint, and several 

 simples must give way before the invasion of chemical 

 products. It is possible that men may succeed in making 

 oil, sugar, and flour, as honey, butter, and jellies are 

 already made, without employing organic substances. 

 Nothing, for instance, would more completely change 

 agricultural conditions than the manufacture of flour 

 from its known inorganic elements. In the actual state 

 of science, there are still products which will be more and 

 more required of the vegetable kingdom ; these are tex- 

 tile substances, tan, indiarubber, gutta-percha, and certain 

 spices. As the forests where these are found are gradu- 

 ally destroyed, and these substances are at the same time 

 more in demand, there will be the greater inducement to 

 cultivate certain species. 



These usually belong to tropical countries. It is in 

 these regions also, particularly in South America, that 

 fruit trees will be more cultivated — those of the order 

 Anonacese for instance, of which the natives and botanists 

 already recognize the value. Probably the number of 

 plants suitable for fodder, and of forest trees which can 

 live in hot dry countries, will be increased. The addi- 

 tions will not be numerous in temperate climates, nor 

 especially in cold regions. 



From these data and reflections it is probable that at ■ 

 the end of the nineteenth century men wiU cultivate on j 

 a large scale and for use about three hundred species, j 



