VEGETAHLE PHYSIOLOGY. 
17 
Not a tree, 
A plant, a leaf, a blossom, but contains 
A folio volume. We may read, and read, 
And read again, and still find something new^; 
Something to please, and something to instruct, 
Ev’n in the humblest weed.” 
The study of vegetable physiology, dis- 
closes to us that all plants are formed of a 
net work of matter called vegetable tissue. 
This substance is arranged in cells, which 
are laterally unconnected with each other, 
but in many instances prolonged vertically. 
These cells are frequently lined with spiral 
fibres. The simplest forms of the flower¬ 
less classes of plants are entirely thus com¬ 
posed, the surfaces being covered with a 
skin also thus constituted. The greater 
number of plants, including all save the 
lowest forms of cryptogamia, have an ad¬ 
ditional modification of structure, viz., tu¬ 
bular vessels, interspersed through their 
system; and hence such a composition is 
styled vascular. Nor are these appearances 
exhibited by the soft portions alone, the 
densest wood is made up of elongated cells, 
hardened by the accretion of solid matter, 
arranged in bundles or layers, and penetra¬ 
ted l)y various vessels. 
B 5 
