the Vasa propria, and Recejjtacles of the Juices of Plants. 273 



to escape from a number of points disposed circularly and con- 

 centrically betwixt the cortical layers, and separated by the 

 thickness of those layers in such a manner that these latex- 

 carrying canals appear to be limited to the external aspect of 

 the several cortical layers. The juices of the outer layers arc 

 somewhat yellow, at least at the period when I have examined 

 them (between November and February), whilst those which 

 exude from the outer aspect of the innermost layers of the bark 

 have a pure white hue. These juices thicken and coagulate with 

 much rapidity, and are very glutinous. They are contained in 

 lacunae of smaller size, less apparent and less regular in character 

 than those met with in the stem. Their cavity is very visible 

 in the external layers, but very much smaller and even quite 

 inappreciable in the internal ; so that these lacunse are no longer 

 distinguishable except by the opake speck formed by the milky 

 juice. They are surrounded by large, short, rectangular cells 

 filled with rounded granules of variable size. These cells are 

 placed end to end in such a manner as to resemble wavy fibres 

 united in a network ; but these fibres form bundles less defined 

 than those in the stem, so that the lacunae also are less regularly 

 circumscribed than their like in the stem, and no longer present 

 the appearance of cylindrical canals with cellular walls ; for the 

 tissue that surrounds them is confounded with that adjacent to 

 it. Besides these cells filled with numerous and large granules, 

 a thin tissue is often discoverable immediately around the lacunse, 

 either empty or occupied with a yellowish granular matter, appa- 

 rently a special secretion [" proper juice "] . Sometimes, how- 

 ever, the cavity of the lacunse is immediately enveloped by a 

 tissue of rounded granules, the thin tissue failing, at least, at 

 parts. 



If a drop of the milky liquid be placed on a piece of moistened 

 glass, although it be partially coagulated, it is seen (at least from 

 November to February) by the microscope to be composed of a 

 multitude of globular granules, of all sizes, identical in appear- 

 ance with those which fill the cells adjoining the lacunae ; and 

 the impression is, that these latter contain a proper juice sepa- 

 rated into globular particles. However, it can be shown that 

 the grains in these cells are starch-corpuscles ; for, when com- 

 pressed or rolled about under the microscope, they are found to 

 retain their globular shape, and are moreover turned blue when 

 moistened with tincture of iodine ; whereas the globules of lati- 

 ciferous juice coalesce when placed between two pieces of glass 

 and subjected to a gliding or rolling movement, and, further, 

 instead of being coloured blue with iodine, they acquire only a 

 yellowish tint. The tincture of iodine has often, moreover, the 

 peculiar efiFect of inducing a remarkable segmentation in them. 



