118 PHARMACEUTICAL BOTANY 
cells, like those of parenchyma tissue, contain cytoplasm and a 
nucleus, and frequently chloroplasts. It remains alive after 
maturity (Fig. 58). Collenchyma is generally found under- 
neath the epidermis in the elongating parts of many stems, less 
often in the midribs and petioles of leaves, and gives support 
to these regions. It is the first strengthening tissue to develop 
in stems. It is frequently observed forming the “ribs’’ of stems 
and fruits of the Parsley Family and ‘‘ribs”’ of stems of the Mint 
Fic. 59.—Stone cells from different sources. 1, From coffee; 2, 3, and 4 from 
stem of clove; 5 and 6, from tea leaf; 7, 8 and 9, from powdered star-anise seed. 
(Stevens, after Moeller.) 
Family. In many leaves it has been found as the supporting 
and strengthening tissue between the stronger veins and the 
epidermis. 
ScLERENCHYMA or stony tissue comprises a variety of support- 
ing elements having thickened cell walls usually composed of 
lignocellulose. When first formed these cells resemble those of 
ordinary parenchyma in having walls of pure cellulose, but later 
lignin, a hard, woody substance, becomes deposited on the inner 
surface of the walls in one or more layers. (Occasionally, as 
in the bark region of stems of Flax and Mezereon, no lignin is 
