ANTHOPHYTA. 263 



leaves. Nearly all the first-formed bundles are of the kind 

 termed "common bundles"; that is, they extend on the 

 one hand into the leaf, and on the other down into the 

 stem. 



499. The general arrangement may be illustrated by Fig. 

 155 in which there pass down from each leaf three bundles; 

 at the lower internode these are, on the left, a, I, c, and, 

 on the right, d, e, f. At the next internode, where the 

 leaves stand at right angles to the lower ones, there are 

 three bundles again, ff, 7i, i, and k, I, m; these are largest 

 at their points of curvature, and they dwindle in size as 

 thfey pass downward and finally unite with the bundles 

 from the lower pair of leaves. The bundles from the 

 third internode pass downward, and in like manner join 

 those from the second pair of leaves, and so on. Thus in 

 such a stem every bundle passes downward through one 

 internode before joining another, and in any internode all 

 the bundles are derived from the leaves at its summit. In 

 many stems, however, the bundles pass down through more 

 than one internode before they join one another. 



500. In some Angiosperms the bundles in a cross-section 

 of a stem are separate from one another, while in others 

 they soon become connected by a cambium-ring as in the 

 Gymnosperms. In the perennial species this gives rise to 

 a marked difference in the structure of the stem (Fig. 156, 

 A and B). 



501. The tissues of Angiosperms are the most varied 

 and highly developed of any in the vegetable kingdom. 

 Not only is every tissue abundantly represented, but each 

 one shows almost numberless more or less well-marked 

 varieties. Moreover, the structures which they form, as 



