160 



MECHANICAL SYSTEM 



fruit as is performed by stone-cells in the case of bark. A similar 

 explanation possibly accounts for the presence of stone-cells in the 

 fleshy tuberous roots of Paeonia, Dahlia, etc. Cells of the same nature 

 are also found in the pith of certain woody plants. 



Rod-shaped sclerenchymatous cells (macrosclereides) with truncated 

 ends (Fig. 51b) are also of frequent occurrence in the bark of trees (e.g. 

 Cinchona), and are very prevalent in pericarps and seedcoats, where they 

 are often arranged at right angles to the surface to form so-called 

 palisade-sclerenchyma (L.EGUMINOSAE, Cannabis, etc., Fig. 51 c). Closely 



V 



Fig. 51. 



A. Sclerenchymatous cell from a walnut - 

 shell. B. Rod-shaped sclereide from the stalk 

 of a pear. C. Element of the palisade- 

 sclerenchyma from the testa of Phaseolus 



vulgaris. 



Fig. 52. 



Columnar sclereide from 

 the leaf of Hakea suaveolcvs 

 together with part of the 

 surrounding palisade - tis- 

 sue. 



related, as regards the shape of the cells, are the bone-shaped osteo- 

 sclereides with dilated and sometimes branched ends, and the I- or 

 T-shaped columnar sclereides or buttress-cells which occur, for instance, 

 in the leaf of Hakea (Fig. 52). Astrosclereides (ophiuroid cells, 

 spicular cells) are multi-radiate sclereides with their branches attenu- 

 ated in a prosenchymatous manner. Cells of this type are found both 

 in bark (Abies pectinata, Larw curopaea) and in the green mesophyll of 

 certain leaves (Camellia, Olca, Fagraea, Dammara, Sciadopiiiys, Gnetum, 

 etc., Fig. 54); in the latter case they help to stiffen the leaf, being 

 indeed partly responsible for the tough leathery nature of that organ. 

 Mention must finally be made of the unbranched sclereides, resembling 

 bast-fibres in shape, but differing from them in the circular [cross- 

 sectional] outline of their pits, which occupy the central axis of the 

 glandular hairs borne by the leaf-blades and petioles of Begonia 

 impe?'ialis (Fig. 53). The coarse villi or shaggy hairs of the Mela- 

 stomaceae often contain whole bundles of sclereides, which penetrate 



