DEVELOPMENT OF PLANTS 



385 



throughout all parts of the leaf (Fig. 277). The stems are com- 

 posed largely of parenchyma, through which are scattered numer- 

 ous veins or vascular bundles derived entirely from the leaves 

 (Fig. 278). These bundles do not develop a cambium (Fig. 60) 

 and consequently the stem does not increase materially in diame- 

 ter, and usually it is columnar in appearance. In many instances 

 the stems are reduced in size and are subterranean, the bulb and 



Fig. 277. 



Fig. 278. 



Fig. 277. Leaf of Solomon's seal with closed venation, entire margins, 

 and sessile upon the stem, i. e., without petiole. 



Fig. 278. Cross-section of stem of rush: v, vascular bundles; st, stereome. 



rhizome being common forms of stems which send up annually 

 short-lived aerial branches. As a rule the stems do not branch, 

 owing to the failure of the buds in the axils of the leaves to 

 develop. 



The flowers are also of rather simple and uniform structure, 

 in the simplest cases being imperfect and consisting of either 

 spirally arranged stamens or pistils without perianth. In the 

 higher types spiral flowers with perianth and both kinds of sporo- 

 phylls appear, and these give place to forms in which the organs 

 are arranged in successive whorls of three parts each, the latter 

 type of flower being especially common. Perigynous, epigynous 

 26 



