!)0 ATLAS OF BIOLOGY. 



No attempt has been made in any of the above figures to represent the starch present. 

 It will be found to vary in quantity with the season of the year. 



Staining is unnecessary, but if resorted to, haematoxylin is preferable. 



FIG. XI. A typical cell of the parenchyma. 



FIG. XII. A cell from the sub-epidermal tissue. 



Both of the above were teased up in eosin, from spirit material. 



FIG. XIII. A typical cell of the sclerenchyma. 



FIG. XIV. Portions of a protoxylem vessel. 



Torn fragments of the thin, unlignified part of the cell wall are often visible, as at *. 



FIG. XV. A small scalariforrn tracheid, one portion of which is drawn in section. 



FIG. XVI. A small portion of the boundary wall between two scalariform tracheides, 

 highly magnified. Gundlach's j^th immersion. 



FIG. XVII. A sieve-tube. 



(Figs. XI. to XV., and Fig. XVII., are all drawn to the same scale, and in XIV., XV., 

 and XVII., the thickened parts of the cell walls are alone shaded. D. 4. 



Figs. XIII., XIV., XV. and XVII. are drawn from cells isolated away under treatment 

 with nitric acid). 



FIG. XVIII. Portion of a sieve-tube from the fresh stem, treated with J p.c. osmic 

 acid. 



The protoplasmic connections figured are inserted from De Bary (132). Gundlach's 

 T T 5 th immersion. 



FIG. XIX. Median longitudinal section through the apex of the rhizome. 

 The apical mass of indifferent tissue which graduates off into the several constituents 

 of the stem, is shaded darkly. A. 2. 



FIG. XX. A portion of the above highly magnified, showing the apical cell, and the 

 two cells of the indifferent tissue last cut off from it. Of these, the older had subsequently 

 divided up. D. 4. 



FIG. XXI. Transverse section across a similar apex. Details as for Fig. XX. D. 4. 



