Others, as, for instance, those of the Pea, Pansy, Bedstraw, &c., which assist in performing the ordinary function of leaves, live as long as, and drop with, the leaves to which they belong.

Lastly, there are some, though they are exceptional, which survive the rest of the leaf and protect the next succeeding bud, as, for instance, in Petteria (figs. 35, 36); or they may last indefinitely, as in Robinia.

In certain cases most of the stipules of a species are caducous, while some of them are persistent.

Thus, in the Black Poplar (Populus nigra), (fig. 37) the stipules of the upper leaf often survive the leafblade, which drops off in autumn, while they retain their place and protect the young bud through the winter.

When stipules survive the rest of the leaf to which they belong, this generally has reference to the protection of the buds. Thus, in Magnolia Umbrella the leaf terminating each year's growth is small, and eventually the blade becomes disarticulated just above the stipules, which are adnate to the leaf-base and enclose the bud (fig. 38). These stipules are in this species the only ones which survive the leaf-blade.

Some other species of Magnolia-for instance, a garden hybrid, M. Soulangiana-agree with M. Umbrella in these respects.

In some cases, however, as in the so-called Acacia (Robinia), the thorny stipules assist in the protection of the plant as a whole.

FIG. 38.-MAGNOLIA UMBRELLA, showing disarticulation of the leafstalk above the stipules, which are wrapped round the terminal bud. Before and after the fall of the leaf.

P, pedestal or persistent base of petiole.

St-E

すす

FIG. 39.

FIG. 40.

PORTION OF SHOOT OF ASTRAGALUS CHINENSIS, showing stipules (St)

connate at the base. Nat. size.

FIG. 39.-Front view. FIG. 40.-Side view. Two leaflets of the compound leaf

are shown.

Where stipules are present the leaf has two, one on each side. Sometimes, however, the two stipules are connate, i.e., have grown together. This may take place on the outside of the leaf, and be either confined to the base, as in a Chinese Astragalus (Astragalus chinensis), (figs. 39, 40), or continue for the greater part of their length, as in Hedysarum esculentum (figs. 41, 42), where

HEDYSARUM ESCULENTUM. Nat. size.

FIG. 41. Apex of growing shoot, showing side view of stipules; L', youngest, partly expanded leaf, with the lowest pair of leaflets still folded, and the stipules, st', connate opposite the leaf-base; L", next younger leaf pushing out of the bud with its stipules, st".

FIG. 42. The same showing the dorsal aspect of the connate stipules, st'.

they are reddish brown and membranous, and develop early, so that the leaves at this stage lie between two rows of stipules. In Sainfoin (Onobrychis sativa) (figs. 43, 44) also the stipules are united for the greater part of their length. In other species they are ' intrapetiolar,' more or less connate on the axillary side of the leaf, as in the Pondweed (Potamogeton) (fig. 45) and in the Knotweeds (Polygonum) (fig. 46), where they form the sheath, called technically an ocrea.

The Hop also has connate stipules, but in this case the two which have coalesced belong to two opposite leaves (figs. 47, 48). Such stipules are termed 'interpetiolar.'

ONOBRYCHIS SATIVA, showing stipules (St) united for the greater part of their length.

FIG. 43.-Side view. FIG. 44.-Back view. P, leaf-stalk; FL, a flower-bud.

In Spergularia (fig. 135, p. 88) the stipules are free from the leaves, but connate at the base, forming a sheath, which envelops the base of the leaves.

De Candolle observes that the existence of stipules