154 



PART II. — VEGETABLE HISTOLOGY. 



(3) Sclerotic tissue. The cells of this tissue are commonly- 

 called stone or grit cells. It differs from ordinary parenchyma 

 in having the walls 

 of the cells exces- 

 sively thickened — 

 so much so, fre- 

 quently, that the 

 cavity of the cell is 

 nearly obliterated. 

 Every gradation, 

 however, may be c 

 observed between 

 these and ordinary 

 parenchyma cells. 

 The cells repre- 

 sented in Fig. 400, 

 though still prop- 

 erly called paren- 

 chyma, are verging 



Fig. 402. Fig. 403. 



Fig. 401.— Portion of epidermis and sub-lying collenchyma from the petiole of the 

 Summer Grape. Transverse section: ej>, epidermis; c, collenchyma cells. Magnified 280 

 diameters. 



Fig. 402. — Portion of epidermis and collenchyma from stem of Rumex crispus. Trans- 

 verse section, magnified 480 diameters: ef>, epidermis; c, collenchyma. 



Fig. 403. — Sclerotic cells from the root of Apocynum androsaemifolium ; magnified 

 about 225 diameters. 



