THE STEM. 



lOI 



shapes, such as hairs, scales, and the hke (figs. 113, 114; 

 see also figs. 361-365). 



129. 2. The cortex. — In some plants the cortex under- 

 goes an enormous development, forming in some tubers the 



greater part of the massive stem. 

 In other plants the cortex under- 

 goes such reduction that it con- 

 sists only of two or three layers of 

 cells. It very commonly enters 

 with the epidermis into the for- 



FiG. 113. — Forms of hairs from Plcct-rantlm s. n, simple pointed hair; d, stalked 

 glandular hair; c, sessile glandular hair with secretion covering tjie two glandular 

 cells. Highly magnified. — After De Bary. 



Fig. 114. — T-shaped hair of the wall-flower {C/iciranthus). e, epidermis. Highly 

 magnified. — After De Bary. 



mation of outgrowths, which are then known as emergences. 

 These emergences may take the form of rounded elevations, 

 producing a warty stem, or they may be sharp pointed 

 and either straight or curved, forming prickles (figs. 115, 

 116); or the emergence may be produced along a con- 

 tinuous line, giving rise to wings upon the stem; or the 

 stem may be more or less co\'ered with large pointed or 

 angular elevations, called tubercles, as in some cactuses 

 (fig. no). Very frequentl}- the intercellular spaces of the 

 cortCN; are greatly enlarged, forming air passages of con- 

 siderable size. These passages may arise by mere separation 

 of the cells of the cortex, or by the destruction of those in 

 certain regions, or by a combination of these causes 

 (fig. 117). In other cases the cortical cells, instead of 



