228 THE SOLID COMPONENTS OF PLANTS. 



their coats being in many cases transparent, and the 

 fluids contained in them colorless, we are obliged, in 

 order to render them more evident, to have recourse 

 to colored fluids, which are readily observed when the 

 cut ends of twigs or branches are immersed in them ; 

 and the course of the vessels through the branch is 

 thus marked by the color. The most eligible fluids 

 for this purpose are decoctions of Brazil wood, and 

 infusions of the skins of black grapes ; the plants like- 

 ly to yield the most satisfactory results to the beginner, 

 are the Periploca gntca, the Aristolochia Sipho, or 

 Dutchman's Pipe, and the young shoots of the Poke 

 (Phytolacca decandra). The plant or twig to be thus 

 injected should be cut with a very sharp knife, and 

 its divided end immediately placed in the colored in- 

 fusion in a warm temperature : after a few hours the 

 color, in plants favorable for the experiment, may be 

 traced into the leaves, the flowers, and even the fruit. 

 This discovers the course of the conducting or adducent 

 vessels ; and when the operation is reversed, the twig 

 being cut at its top, and inverted in the colored fluid, 

 we can trace that of the returning or abducent vessels. 

 By placing transverse and longitudinal sections of 

 twigs and parts of herbaceous plants thus treated un- 

 der the microscope, we are able to ascertain the or- 

 ganization of the coats of the vegetable vessels. Some 

 of the vessels, however, cannot be rendered more vis- 

 ible by this means, as they refuse to admit colored 

 fluids, and therefore any knowledge of their structure 

 can be obtained only by means of powerful micros- 

 copes. 



The Vascular or tubular portion of the vegetable 

 structure composes a kind of net-work, owing to the 

 frequent communication or anastomosis of the vessels 

 with one another, which pervades almost every part of 

 the plant. The particular vessels vary both in form 



