98 ATLAS OF BIOLOGY. 



FIG. XI. Median longitudinal section of the epicotyledouary axis of Fig. V. x 10. 



FIG. XII. Transverse section of the same, across the point marked * * in Fig. V. 

 x 10. 



FIG. XIII. A similar section across the same axis of an older plant, x 5. 

 (In Figs. XI. to XIII. the cambium layer is represented as a black line.) 



FIG. XIV. The bundle-system of the French Bean, seen from the side. Dissected 

 as for the Fern, Fig. VI., Plate XXI. From nature, after Nageli. See De Bary (132).* 

 The bundles of the left side are shaded darkly, x 2. 



FIG. XV. Thin transverse section of a portion of Fig. XII. 



The protoxylem elements, xy'., may often be at once recognized in transverse sections, 

 as the spiral or annular thickenings frequently tear away in cutting and hang ragged. D. 3. 



FIG. XVI. Kadial-longitudinal section of a similar stern, taken through the axis of a 

 young bundle. D. 3. 



FIG. XVII. Portion of a thin transverse section of Fig. XIII. 



The phloem parenchyma and the rays of the vascular bundle are here shaded. D. 2. 



In Figs. XV. and XVII., the trichomes are for the most part omitted, and no note is 

 taken of the chlorophyll present in the cells of the parenchymas. 



The only structures in which the protoplasm is drawn, are the sieve tubes ; it is repre- 

 sented in them in the contracted post-mortem, state. (See below.) 



FIG. XVIII. Sections of the sieve tube in the above. 

 i. The protoplasm, drawn as in life. 



ii. The protoplasm, drawn in the shrunken post-mortem condition, 

 iii. Portion of a sieve-tube bearing both transverse and lateral sieve plates. Iodine. 

 Gundlach's /gth immersion. 



FIG. XIX. A cambium cell, isolated under treatment with nitric acid, as for the fern- 

 stem, Figs. XIV., etc., Plate XXI. D. 3. 



FIG. XX. A similar cell, as seen in tangential section of the cambium layer. D. 3. 



FIG. XXI. -A dividing cambium cell, drawn from the layer, cb'., of Fig. XVI., as seen 

 in radial-longitudinal section. D. 3. 



* Largo models of this and certain other bundle-systems, after Nageli and others, are made by H. Gasser, of the 

 Botanical Institute, Graz. 



