STRUCTURE OF VEGETABLES. 55 
the most simple forms of vegetation consist of a congeries 
of cells (cellular tissue) of the same kind, and have no 
visible fructification ; such are the sea-weeds (alga, con- 
Jerve, &¢c.), mosses, and lichens. In the more complex 
tribes the cells become variously modified, are elongated into 
tubes or vessels (vascular tissue), some of which possess a 
spiral structure, and others have their sides studded with 
little glands. The vascular tissue consists of two kinds of 
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Lien. 1. SECTIONS OF RECENT VEGETABLES; illustrative of their in ~ 
ternal organization. (From Dr. Lindley.) 
Fig. 1.—Longitudinal Section of Coniferous Wood. 
a. The Ducts. 6. Spiral Vessels. c. Glandular vessels. 
2.—Transverse section of a dicotyledonous stem. 
a. Pith, or central column. 6. The bark. c. Medullary rays. 
d. Vascular tissue between the medullary rays. 
3.—Elongated cellular tissue, forming the medullary rays. 
4.—Transverse section of a monocotyledonous stem. 
vessels. 1. The spiral vessels or trachee: these are mem- 
braneous tubes, with conical extremities, having within a 
coil of elastic fibre spirally twisted, and capable of being 
unrolled (Lign. 1, b.). 2. The duets ; which are a modifi- 
cation of the structure of the spiral vessel ; their extremities 
