Structure of Vegetables , 
m 
Spiral vessels were supposed by Malpighi and Grew 
to be air vessels, performing a similar office in plants, 
to the lungs of animals ; but from the curious experi- 
ments and observations of Mr Knight, it appears that 
the fluids destined to the nourishment of the plant being 
absorbed by the root, are conveyed to the leaves by 
these vessels ; and from their situation near the pith 
he has given them the name of central vessels. 
Seeds*-— The seeds from which the future plant pro- 
ceeds is composed of different parts ; of these parts the 
embryo, or germ, to which Linnaeus gave the name of 
corculum , or little heart, is the most essential. This 
part is sufficiently obvious in some seeds, as the Bean, 
the Pea, and the Lupine ; and its internal structure, 
before the commencement of vegetation, is very simple. 
The cotyledons, or seed lobes, are immediately attach* 
ed to the embryo, and indeed are to be considered as 
forming part of it. In most seeds the cotyledons are 
two in number ; but some seeds, as those belonging to 
the Grass and Corn tribe, the Palms, and some other 
plants, have only one cotyledon, while others have 
three or more ; and hence the division of plants sug- 
gested by this peculiai’ity of structure in the seeds, in- 
to monocotyiedonous, dicotyledonous and polycotyledo- 
nous. In those plants the seeds of which have only 
one cotyledon, the greater part of the substance of the 
seed is composed of a farinaceous, fleshy, or horny sub- 
stance, called albumen or white. When seeds of this 
description germinate, the cotyledon never rises out of 
the ground, or performs the office of leaves ; but in 
plants whose seeds have two cotyledons, they rise out 
bf the ground, and being formed from the seed itself, 
11 3 
