236 PRINCIPLES OF BOTANY, ETC, 
| § 232. 
Chemistry makes us acquainted with the com. 
ponent parts of vegetables, but Anatomy explains — 
their wonderful structure, to which we now there- 
fore direct our whole attention. 
The last science has detected the following differ- 
ent vessels in plants: Adducent vessels, (Vasa addu- 
centia) ; reducent vessels, (Vasa reducentia) ; air ves- 
sels, (Vasa pneumato-chymifera) ; lymphatic vessels, 
(Vasa /ymphatica); cellular texture, (Tela cellulosa), 
Vhey may be all observed with a microscope when 
injected. ‘This can easily be accomplished by put- 
ting a plant in a decoction of brazil-wood, (Czsal- 
pinia echinata); which fills the adducent and air 
vessels. The reducent vessels only appear, when the 
plant is cut at the top, and put inverted in the liquid. 
‘The lymphatic vessels, may be seen without injecting 
them, merely by carefully taking off the epidermis 
and putting the plant under the microscope. ‘The 
other vessels, however, except the air vessels and 
adducent vessels, can yery seldom be filled with co- 
loured liquid. | 
Gessner and others, who paid great attention to 
the Physiology of plants, have proved the presence 
of all these vessels by means of the airpump. And 
only lately, Mr Achard tried to inject plants, which 
the animal and vegetable principles, and partly destitute of 
proper means to separate and analyse them accurately. The 
nature of the extractive, dying, bitter, acrid and narcotic prin- 
ciples and their varieties, and many others, is still unknown 
fo US. 
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