64 



MOEPHOLOGY OF THE CELL. 



sentecl by the parenchyma cells just under the epidermis, or 

 outer layers of cells, in many plants. The cell-wall is thickened 



a b 



very considerably at the angles, and upon the application of 

 dilute acids swells greatlj-, but without becoming clearly muci- 

 laginous. When moist, 

 such cells have a bluish- 



0?^ 



44 



white color and a marked 

 lustre. They are known 

 as 



216. Collenchyma cells. 



They are generally some- 

 what elongated, and so 

 united as to form threads 

 which possess great 

 strength, and are believed 

 to serve an important me- 

 chanical office in the plant. 

 Good examples of these 

 are afforded by the stems 

 of manj' Umbelliferae. 



EPIDERMIS. 



217. This is the outermost layer of cells covering the sur- 

 face of the plant. In some of the higher plants it persists with 

 little change throughout the life of the organism ; in others it is 



Fig. 43. Pavencliyma with wnlls which have undergone the gelatinous modification: 

 a, from tlie centre of the style of Salvia scabiosaefolia ; b, from the stigma of Gesneria 

 elongata. (Capus.) 



Fio. 44, Transverse section of root-stock of Smilaclna bifolia, showing collenchyma 

 cells just under the epidermis, ep. Note also the ordinary parenchyma atpc, and the 

 endodermis at ap. (Van Tieghem.) 



