528 SIR JOHN LUBBOCK ON STIPULES, 
SALICINES. 
Populus balsamifera, Linn., var. viminalis——The winter-bud of 
Populus is protected by the stipules, which secrete and exude a 
considerable quantity of gum during autumn, and cover the 
younger ones, especially at the edges, binding the whole bud 
firmly together, throwing off the wet, and no doubt in itself 
acting as a protection to the strongly involute and tender leaves, 
which even at this period are of considerable size. 
The outer and oldest pair are connate in one piece, which is 
firm and rigid in the centre, with broad, more or less membranous 
margins extending round the greater part of the bud, but less 
than half its length. The second pair are also connate, rather 
more membranous, extending round the bud till their edges almost 
meet at the base, and nearly as long as the bud. The third pair 
are connate, convolute, extending a little beyond the bud, which 
they completely cover at the top. They are stiffly membranous, 
but green, and completely covered with gum on both surfaces. 
The second and third pairs completely cover the bud, and, when 
removed, expose the first two leaves. They themselves have no 
leaves. 
The first and second leaves lie in a furrow or groove where 
their stipules meet. The fourth pair of stipules are free, sub- 
ulate-linear, with a strong and conspicuous midrib, lying in front 
of their own leaf, and overlapping by their edges as well as over- 
lapping the posterior edges of the fifth or next younger pair. 
The fifth pair are precisely similar to the fourth, but smaller, 
and the fourth and fifth pairs completely cover the bud. Both 
pairs are considerably longer than their own leaves. The sixth 
pair are very much smaller, and only about two-thirds the length 
of their leaf. The seventh pair are even smaller, and only about 
one-third the length of their leaf. Both leaves have attained 
@ proportionate size with their stipules such as they maintain 
when expanded in summer. 
In Populus nigra, Linn., var. dilatata, Ait. (syn. P. fastigiata, 
Desf.), the leaves are alternate, petiolate, stipulate, deltoid, 
crenate, strongly involute in bud, and gummy, glabrous, de- 
ciduous; the petiole laterally compressed, but in the bud-state 
nearly terete, or altogether undeveloped in very early stages, and 
gummy. 
The stipules are more or less boat-shaped or keeled or con- 
