72 



BOTAI^r. 



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 nre extremely irregular. 

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

 (e.g., in the sclerenchyma-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 tlie rhizome of Pteris aguiiina, in 



FiQ. 56A 



Fie. 56.— Two sclerenchyma-cells from the hypoderma of the rhizome of PterU 

 aguUinay isolated by Schulze's maceration. .4, a very thick-walled cell, with branch- 

 ing pits; J5, 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 Pinus pinaster, transverse stction. c, cuticularized layer 

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

 wall of marginal cell ; g, i'. hypoderma of elongated s lereuchyma ; jj, chlorophyll- 

 hearing parenchyma ; pr, contracted protoplasmic contents. X IjOO.— Af ler Sachs. 



Tvhich 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). 



(6) 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- 

 renchyma-cells, which at first sight might easily be mistaken for bast 

 fibres (Fig. 57, fi', i). The hypoderma of many other plants appears to 

 be of a similar nature. 



