464 Theory of the Nutrition [BOOK in. 



which it runs V These passages taken with those quoted above 

 show that Aristotle made the substances required for the 

 growth of plants reach them from the earth ready elaborated, 

 as has been before observed ; and this view, still maintained in 

 Mariotte's time, may yet be met with among those who are 

 ignorant of physiology. It is interesting then to see, how 

 vigorously Mariotte exposes the incorrectness and absurdity of 

 this idea, though he has no new discovery to help him. In his 

 third hypothesis he maintains, that the salts, earths, oils, and 

 other things, which different species of plants yield by distilla- 

 tion, are always the same, and that the differences are due 

 entirely to the way in which these principes grossiers and their 

 simplest parts are united together or separated, and he proves 

 it thus : If a bon-chretien pear is grafted on a wild one, the 

 same sap, which in the wild plant produces indifferent pears, 

 produces good and well-flavoured pears on the graft ; and if 

 this graft has a scion from the wild pear again grafted on it, 

 the latter will bear indifferent fruit. This shows that the same 

 sap in the stem assumes different qualities in each graft. But 

 still more forcible is his proof of the fact, that plants do not 

 take their substance direct from the earth, but produce it 

 themselves by chemical processes. Take a pot, he says, with 

 seven to eight pounds of earth and grow in it any plant you 

 like ; the plant will find in this earth and in the rain-water which 

 has fallen on it all the principles of which it is composed in its 

 mature state. You may put three or four thousand different 

 kinds of plants in this earth ; if the salts, oils, earths were 

 different in each species of plant, all these principles must be 

 contained in the small quantity of earth and rain-water which 

 falls upon it in the course of three or four months, which 

 is impossible; for each of these plants would yield in the 

 mature state a dram of fixed salt at least and two drams of 



1 See the Fragments of Aristotelian phytology in Meyer's ' Geschichte der 

 Botanik,' i. pp. 119, 125. 



