THE SOLID COMPONENTS OF PLANTS. 233 



face. They have been detected, also, in the calyx, 

 and other parts of the flower ; and Gaertner asserts 

 that they are evident even in the seed-lobes. The 

 spiral vessels, in their course, proceed always in straight 

 lines, without any deviation ; whereas all the other 

 vegetable vessels often take a curved direction. It is 

 into these vessels that colored injections most easily 

 enter ; and when an annual twig of the Fig is thus 

 injected, they are seen in a transverse section of it, 

 like red dots around the pith, placed within an exter- 

 nal circle of the vessels, which contain the proper or 

 milky juice of the plant. 



These varieties of form in the vegetable vessels are 

 not such important differences essentially as the arte- 

 ries and veins of animals ; for in some plants, accord- 

 ing to Mirbel, the 3 different modifications of struc- 

 ture are found to take place in the same tube. In the 

 Butomus umbellatus, or flowering Rush of Europe, 

 the same author says, " I have seen long portions of 

 vessels present, at intervals, the appearance of an un- 

 rolled trachea (or spiral vessel), a transversely cleft 

 vessel, and a porous one. 



Mirbel mentions another set of vessels, which he 

 denominates little tubes; but they appear rather as 

 tubular cells, being closed at the extremities. They 

 resemble stretched cellular substance, except that the 

 membrane composing them is less transparent, and of 

 a greater consistence. The solidity of plants depends 

 very much on the quantity and density of these cells, 

 which are filled with thick and colored, or diin and 

 colorless juices, according to the nature of the plants 

 in which they exist. 



The structure of the internal Glandular texture of 

 vegetables is much more difficult of demonstration 

 than that of any of the general solid components which 

 20* 



