268 



HOW CEOPS GEOW. 



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 difierenoes in the structure of their stems and 

 seeds. These are, 1, Endogenous or Monocotyledonous ; 

 and, 2, Exogenous or Dicotyledonous plants. As regards 

 their stems, these two classes of plants difier in the ar- 

 rangement of the vascular or woody tissue. 



Endogenous Plants arc 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 J 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- 



Fis. 47. 



formly throughout the section, though less abundantly to- 

 wards the center. On splitting the fresh stalk lengtliAvise, 

 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, ov plexus. In a ripe maize-stalk which is 

 exposed to circumstances favoring decay, the soft cell-tis- 

 sue first sufiers change and often quite disappears, leaving 



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