74 
+> an 
84. Structural and Physiological Botany. = 
ordinary leaves, or by some of special form which are con- 
sidered as stipules, as in the alder. The bud-scales usually 
fall off when the bud begins to swell in the spring andthe 
enclosed parts to grow ; but in some cases, as the oak and 
beech, they continue to grow for some time at the base. | 
The stem-bud is a compressed image of the stem, on 
which account the peculiar position of the organs which are 
attached to it can be especially well studied in the bud by 
making a transverse section through it. | 
The relative position of the bud-scales, fohage-leaves, 
sepals, and petals, in the bud, or, as it is termed, their @s-_ 
tivation, is usually zmbricate, where the margins of contiguous 
leaves overlap one another, less often va/vate, as in the 
calyx of the mallow (Fig. 124), where they merely touch one 
F IG. ey wee Valvate Fic. 125.—Redupli- Fic. 126.—Indupli- Fic. 127.—Enfolding 
estivation; calyx cate valvate zstiva- cate valvate zstiva- zestivation. 
. of mallow. tion. tion. 
another by their edges. The most important modifications: 
of the imbricate eestivation are the enfolding (Fig. 127) in 
which one leaf entirely encloses another, the vexc/ary (Fig. 
128), peculiar to the Papilionaceze, where one leaf much ~ 
larger than the rest encloses the others ; adternate, as in the 
tulip (Fig. 129), where two rows of floral leaves alternate 
regularly with one another, and guzncunctal, as in the wood- 
sorrel, the calyx of the rose, the calyx and corolla of the — 
buttercup, &c. (Fig. 130), where the five leaves are so placed 
that between two outer ones which are entirely uncovered 
and two inner ones which are entirely covered, there lies a 
fifth (leaf 3), so inserted that with one of its margins it overs -@ 
laps one of the two inner leaves, while the other margin is 
