72 BOTANY. 



considerable extent. The cells are usually short, but in some 

 cases they are greatly elongated ; they are sometimes regular 

 in outline, but more frequently they are extremely irregular. 

 They do not contain chlorophyll, but in some cases at least 

 (e.g., in the scleienchyma-cells in the pith of apple-twigs) 

 they contain starch. 



Sclerenchyma occurs in Bryophytes, Pteridophytes, and 

 Phanerogams. 



(a) Good specimens of sclerenchyma may be obtained for study by 

 making longitudinal sections of the rhizome of Pteris aquilina, in 



Fio. 565. 



FIG. 56^4. 



Fio. 57. 



Fig. 56. Two eclerenchyma-cells from the hypoderma of the rhizome of Pteris 

 aquilina, isolated by Sclmtze's maceration. A, a very thick-walled cell, with branch- 

 ing pits; B, a cell with walls less thickened the wall of the opposite side of the 

 cell is seen to be filled with numerous pits. X 500. After Sachs. 



Fig. 57. Margin of leaf of PinusjAnaster, transverse section, c, cuticularized layer 

 of outer wall of epidermis ; i, inner non-cuticularized layer ; c', thickened outer 

 wall of margin il cell ; g, i', hypoderma of elongated s lerenchyma ; j>, chlorophyll- 

 bearing parenchyma ; pr, contracted protoplasmic contents, x 800. After Sachs. 



which it occurs as a thick hypodermal mass ; by boiling in potassium 

 chlorate and nitric acid (Scliulze's maceration) the cells may be com- 

 pletely isolated (Fig. 56, A and B). 



(b) The cells of the medullary rays of woody Dicotyledons e.g., 

 Acer, Pirus, Ostrya, Liriodendron, etc. are generally thick-walled 

 when old. and in this state must be classed as sclerenchyma. 



(c) The hypoderma of the leaves of pines consists of elongated scle- 

 nmchyma-cells, which at first sight might easily be mistaken for bnst 

 fibres (Fig. 57, rj, ). The hypoderma of many other plants appears to 

 be of a similar nature. 



