268 HOW CROPS GROW. 
est herbaceous stems, while they constitute a large share 
of the trunks of most shrubs and trees. From the tough- 
ness which they possess, and the manner in which they 
are woven through the original cellular tissue, they give 
to the stem its solidity and strength. 
The flowering plants of temperate climates may be di- 
vided into two great classes, in consequence of important 
and obvious differences in the structure of their stems and 
seeds. These are, 1, Endogenous or Monocotyledonous ;- 
and, 2, Heogenous or Dicotyledonous plants. As regards 
their stems, these two classes of plants differ in the ar- 
rangement of the vascular or woody tissue. 
Endogenous Plants are those whose stems enlarge by 
the formation of new wood in the interior, and not by the 
external growth of concentric layers. The seeds of endog- 
enous plants consist of a single piece—do not readily 
split into halves,—or, in botanical language, have but one 
cotyledon ; hence are called monocotyledonous. Indian 
corn, sugar cane, sorghum, wheat, oats, rye, barley, the 
onion, asparagus, and all the grasses, belong to this tribe 
of plants. 
If a stalk of maize, asparagus, or bamboo, be cut across, 
the bundles of ducts are seen disposed somewhat uni- 
formly throughout the section, though less abundantly to- 
wards the center. On splitting the fresh stalk lengthwise, 
the vascular bundles may be torn out like strings. At 
the nodes, where the stem branches, or where leaf-stalks 
are attached, the vascular bundles likewise divide and 
form a net-work, or plexus. In a ripe maize-stalk which is 
exposed to circumstances favoring decay, the soft cell-tis- 
sue first suffers change and often quite disappears, leaving 
