264 



A TEXT-BOOK OF BOTANY. 



Calamus the cells are so arranged that very large intercellular 

 spaces are formed (Fig. 134). (^) A number of modifications 

 of typical parenchyma also occur, some of the cells being either 

 quite thick-walled or considerably elongated. The walls of pith- 



G 



Fig. 134. Forms of cells. A. — Transverse section of the pith of Tradcscantia vir- 

 gintca: I, intercellular space; W, cell wall. B. — Transverse section of calamus rhizome 

 showing a large oil-secretion cell, smaller cells containing starch, and large intercellular 

 spaces (T). C. — Transverse section of the stem of Phytolacca decandra showing collenchy- 

 matous cells beneath the epidermis. D. — Longitudinal section of taraxacum root showing 

 branched laticiferous tissue (L). E. — Transverse section of pyrethrum root: R, oil-secre- 

 tion reservoir with oil globules; I, cells with sphere-crystals of intilin, such as separate in 

 alcoholic material; L, cells containing irregular masses of inulin, as found in dried material. 

 F. — Longitudinal section of stem of Cucurhita Pepo: S. sieve-cell with protoplasm-like 

 contents, and transverse walls (sieve plates) showing simple pores. 



parenchyma may consist of lamellae of lignocellulose and mucilage, 

 as in Sassafras pith (Fig. 133). 



Mechanical tissue includes all those cells which serve to 

 keep the various parts of the plant in their proper positions, one 



