THE PRINCIPLES OP BOTANY. 
9 ^ 
tlms the spines of the gorse are either metamorphosed 
branches or altered leaves^ whilst the prickles of roses and 
briars are mostly only abortive leaves. 
We have now to glance at some further modifications of 
leaves, which will not be without significance in the remarks 
which are to follow. These will be reviewed under the heads 
of {a) stipules, [b] bracts, and (c) spathes. 
a. Stipular leaves are placed at the base of the true leaves. 
Sometimes, as in the roses, they are anastomosed with the 
base of the petiole, at others, as in the pea-tribe, they are 
separate and distinct. The yellow vetchling [Lathyrus aphaca) 
when arrived at maturity shows a plant in which the true 
leaves are wholly abrogated; the truth being that the leaves 
are diverted to form tendrils, and the apparent leaves, which 
are large and shield-shaped, are stipulce enlarged to perform 
the leaf function. The whole of this—the papilionaceous 
family of plants—is remarkable for the variation and changes 
in the stipular leaves. 
b. Bracts are metamorphosed leaves situate at the base of 
fiower buds, and may perhaps most readily be seen on the 
scape or flower-stalk of the violet, consisting of a pair of 
minute lanceolate leaves. Leaves of this kind are mostly 
found at the base of each flower-stalk, and its object appears 
to be as a covering and protection to the flower-bud during 
its immaturity. 
c. Spatha are still further developed leaf-organs for par¬ 
ticular purposes, as thus the covering to the bud of the snow¬ 
drop and daffodil are spatha; the expanded flower-like leaf 
surrounding the stamens and pistils of the Arum —lords and 
ladies, or the finer white one, A. Italicum, of the greenhouse 
—is a spatha. The lily tribe is remarkable for this protective 
covering to the flowers, which, like those parts already men¬ 
tioned, can only be considered as modifications of leaves; 
just so are the scales by which young buds are protected, as 
a simple gradation may be traced from the outer scales of the 
buds of the chesniit or ash to the more complicated leaf bud 
in the centre. There is, then, in plants a diversity of orpns, 
and these assume numberless forms, and their modifica¬ 
tions are in reference to that law which is now distinguished 
by the term Morphology, a recognition of the true princi¬ 
ples of which forms the only sound basis of true botanical 
knowledge. This law is so well described by Professor Bal¬ 
four in his Manual of Botany that we make no excuse for 
copying the passage in this place, not only in explanation 
of much we have here advanced, but in anticipation ot 
our next paper on the structure of flowers. 
