CHAP, ii.] of Plants. Christian Wolff. 475 



not contain oil and salt, and there are many from which the 

 oil may be squeezed out ; and oil and salt are found in all 

 plants if they are examined chemically.' He insists on the 

 correctness of the view taken by Malpighi and Mariotte, that 

 the constituents of the food must be chemically altered in the 

 plant. Since every plant, he says, has its own particular salt 

 and its own particular oil, we must readily allow that these are 

 produced in the plant and not introduced into it. But at the 

 same time since plants cannot grow where the soil does not 

 supply them with saline and especially with nitrous particles, it 

 is from these that the salts and oils in the plant must be pro- 

 duced, and the water also changed into a nutritious juice. 

 Further on he alludes to the saline, nitrous and oily particles 

 which float in the air, and says that daily experience shows that 

 most of the substance of putrefying bodies passes into the air, 

 and that if we admit light through a narrow opening into a dark 

 place, we can see a great number of little particles of dust floating 

 about ; water also readily takes up salt and earth, and mineral 

 springs show that metallic particles are mixed with it. There- 

 fore there is no reason to doubt that rain-water also contains 

 a variety of matters which it conveys to the plant. Alluding 

 once more to the chemical changes in the constituents of the 

 food which must be supposed to take place in the plant, he 

 connects the subject with some remarks on the organs of 

 plants, in which he closely follows Malpighi ; he says that these 

 changes cannot take place in tubes, because the sap merely 

 rises or falls in them ; we can only therefore suppose that it is 

 in the spongy substance (the cellular tissue) that the nutrient 

 sap is elaborated, and accordingly the vesicles or utriculi 

 are a kind of stomach ; but the change in the water can only 

 be this, that the particles of various substances which are in 

 rain-water are separated from it and united together in some 

 special manner, and this cannot be effected without special 

 movements. But his ideas on these movements in the sap 

 are somewhat obscure. He employs the expansion of the 



