CHAP, ii.] of Plants. Mariotte. 465 



earth, and all these principles together with those which are 

 mixed with the water would weigh at least from two to three 

 ounces, and this multiplied by four thousand, the number of 

 the species of plants, would give a weight of five hundred 

 pounds. 



These arguments like those of Jung, and in the main also 

 those of Malpighi, rested on facts which were on the whole as 

 well known in ancient times as in the xyth century; but no 

 one had before given heed to considerations, which were 

 in themselves quite sufficient to do away with the Aristotelian 

 teaching on the subject of the nutrition of plants. 



In the second part of his letter Mariotte discusses the 

 phenomena of vegetation which depend on nutrition ; he com- 

 pares the endosperm in the seed with the yolk of the egg in 

 animals, and the entrance of the water into the roots with its 

 rising in capillary tubes; he takes the milky juice to be the 

 nutrient sap and compares it with arterial blood, the other 

 watery juices answering to venous blood. He says something 

 quite new about the pressure of the sap ; he notices the high 

 pressure at which the sap stands in plants, and concludes 

 from it that there must be contrivances in them, which allow 

 of the ingress of the water but not of its egress. The exist- 

 ence of the pressure is well demonstrated by the outflow from 

 plants which contain milky juice when they are wounded, and is 

 compared with the pressure on the blood in the veins. Equally 

 striking is his further conclusion, that the pressure of the sap 

 expands the roots, branches, and leaves, and so contributes to 

 their growth. The sap, he adds, would not be able to remain 

 at this 'pressure, if it did not enter by pores, which forbid its 

 return. In these remarks lay the first germs of speculation on 

 the growth of plants, such as we shall meet with in Hales also 

 in a somewhat different form, but in the backward state in 

 which phytotomy then was they could not at present be further 

 developed ; we shall recur to them further on, though in a 

 different connection. 



Hh 



