THE ANGIOSPERMAE : STEMS 



871 



type, are as a rule only temporary flowering shoots and may have a very 

 narrow cortex or none at all. Such stems may be regarded as being either 

 entirely stelar or else as having no stele. There is at any rate, in many cases, 



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Fig. 856. — Zea rnais. Transverse section of stem showing 

 absence of cortex and vascular bundles in contact with 

 hypodermis. 



I'u.. 857. — Anihriscus syhestris (Umbelliferae). 

 Collenchyma in the cortex of the stem. 



no stelar boundary visible. Where a cortex is present it often contains 

 numerous and small marginal leaf traces. 



The outer zones of the cortex freque ntly form a collenchyma either in a 

 continuous band or, in angular stems such as those of Labiatae and Umbelli- 

 ferae, developed only below the ridges (Fig. 857). Collenchyma is definitely 



