1889-90-] On SclerencJiyviatoiis Cells. 379 



by outgrowths or irregularity of form. The term " scleren- 

 chyma," introduced by Mettenius, and derived from the two 

 Greek words skleros, hard, and enchyma, an infusion, indicates 

 those tissue elements which have not only thickened their 

 walls at the expense of the cell-cavity, but have also lost the 

 cell-quality, or the power to assist in assimilation and nutri- 

 tion. The structure of the walls is in general that of strongly 

 thickened cell-membranes, with their numerous modifications. 

 As thickening and ultimate lignification proceed, the proto- 

 plasmic body and nucleus disappear, and of these, and the 

 products resulting from their activity, only remnants are felt, 

 together with watery fluid, partly as undefined granular 

 contents. 



De Bary divides sclerenchyma into two main forms, which, 

 however, are not always sharply differentiated from each 

 other — viz., (1), short sclerenchymatous elements; and, (2), 

 elongated elements or sclerenchymatous fibres. " Short 

 sclerenchymatous elements " is the term applied to all forms 

 which have not pointed or tapering ends. Under this term 

 come the "stone elements" or stone-cells — the hard con- 

 cretions that are found in the succulent tissue of pears, or in 

 groups in the root-tuber of dahlia and in the pith of Hoya 

 carnosa. Plums, cherries, &c., owe their name of " stone- 

 fruit " to the fact that the fundamental tissue of the pericarp 

 — that is, the transformed wall of the ovary — becomes separ- 

 ated into two layers, or often three, of which the innermost 

 is the so-called " stone." Although consisting at first of thin- 

 walled parenchymatous cells, they become, by the time they 

 are ripened, strongly lignified. Sclerenchymatous fibres of 

 elongated spindle-like shape, with sharp ends, simple or 

 branched, are the form of strengthening tissue, on the other 

 hand, which is universal in Phanerogams. These are fre- 

 quently called " bast-fibres," from the definite region of the 

 cortex in which they occur in dicotyledons. In transverse 

 section these fibres are acutely angular when they are closely 

 united into bundles. In those occurring singly, or found in 

 intercellular spaces or in leathery leaves, they are round or 

 nearly so. In Phanerogams they are freely branched, and 

 their form appears to vary with the special tissue in which 

 they occur, the most varied shapes being met with. The 



