102 PLANT LIFE. 



remaining thin-walled, may become greatly thickened in 

 certain regions, or even throughout the cortex. These 



Fig. 115. Fig. 116. 



Fig. 115. — Prickles on the stem of a rose. Natural size. — After Prantl. 



Fig. 116. — A longitudinal section through a rose prickle in a young stage, showing how 

 the sub-epidermal (cortical) tissues enter into the structure of the emergence. Magni- 

 fied 200 diam. — After Rauter. 



Fig. 117. — Transverse section of the stem of Elatine, showing intercellular canals, c. 

 Magnified about 15 diam. — After Reinke. 



mechanical cells are likely to be aggregated in clusters or 

 strands, and serve an important purpose in strengthening 



