156 PLANT ANATOMY. 
the manner indicated a screw-shaped disposition of the thick- 
ening (Fig. 74). Hofmeister’ found by maceration of these 
fibres in nitric acid and potassium chlorate, and subsequent. 
pressing, a more scale-shaped arrangement of the layers. 
Cells, which have walls of considerable thickness when com- 
pared with the diameter of the lumen (cell-cavity), that is such 
in which the latter is contracted to a very small cleft, are desig- 
nated as dast cells when they are extended in length (Figs. 110 
and 111), or as stone-cells (Figs. 75 and 76°) when they are but 
Fic. 74.—4A, Bast fibres from Cinchona barks, boiled with hydrochloric acid,; P, the 
same softened in ammoniacal oxide of copper after treatment with hydrochloric‘acid, 
(P from Dippel) ; 7, original size of the cell ; s, the swollen layers, 
short. The latter, particularly, show a very distinct stratifica- 
tion of the membrane. ; 
1 « Verhandl. d. Sachs. Gesellsch, d. Wissensch.,” X., 1858, p. 32. 
* They may also be called sclereids (derived from 6%Anp6s hard) in op- 
position to the proper mechanical cells, the stereids (from érepe6s mas- 
sive). Compare Tschirch, ‘“Beitrige zur Kenntnis des mechanischen 
Gewebesystems,” Pringsheim’s Jahrb., 1885, and ‘Ber. d. deutsch. 
botan. Ges., ITI. (1885), No. 2, 
