88 NUTRITION. 



72. In the higher orders of plants, that is in the Mo- 

 nocotyledonous and Dicotyledonous divisions, a particular 

 motion of elaborated fluid is seen taking place in some of 

 those vessels which we denominated, under the division 

 of Anatomy, proper ducts, and to which the term cyclosis 

 is applied. 



73. The fluid contained in' these vessels which ramify 

 amongst most portions of a plant, is denominated latex 

 by Schultz, and milk juice by others ; according to some, 

 it has its origin in the sap before that fluid has been 

 elaborated in the leaves, and then passes into the 

 leaves in order to undergo elaboration itself, from 

 whence it passes over the plant into the bark through 

 the vessels we have named : it consists of two portions, 

 a colourless serous, and a thick consistent coagulable 

 part ; in most cases also it contains a great num- 

 ber of little globules possessed of a peculiar molecu- 

 lar motion, and likewise a number of other bodies of 

 various forms, chiefly composed of starch or gum, the 

 whole latex varying in colour according to the species in 

 which it is examined. 



74. According to Meyen this fluid moves along the 

 proper ducts, (or cynenchyma of authors), which form a 

 continuous anastomosing system of vessels running 

 along the stem, and through the tissue of its various 

 appendages, but most evidently seen in the inner layers 

 of the bark. 



75. The fluid rises in some of the main vessels run- 

 ning in a parallel direction with the course of the stem 

 from the root to the leaves, which latter it traverses by 

 means of the various branches of the vessels, and turns 

 back again through the smallest ones in order to arrive 

 again at the main vessels in the trunk, from thence run- 

 ning to the root which it traverses like the leaves, and 

 there receiving a considerable addition of crude sap 

 commences the same circulation anew. In vigorous 

 plants during the warmer months of the year the mo- 

 tion of the latex is very rapid, and often far quicker 

 than that of the blood of the amphibia ; at a low tempe- 



