certain Tropical Trees . 61 
habit have been put forward by various investigators. 
Potter, in a paper on bud-protection in the tropics 1 , points 
out that the young leaves, by virtue of their disposition in 
a vertical plane, escape much of the damaging effect which 
the powerful perpendicular rays of a tropical sun might pro- 
duce. In Amherstia nobilis , moreover, each pair Qf leaflets 
overlaps to a large extent the pair below, so that the 
surface exposed directly to light is still further reduced. 
Similarly also, in species of Brownea , the massing together 
of the several branches arising from a bud affords a con- 
siderable amount of mutual covering and, if need be, pro- 
tection to the leaves. Potter, assuming that the extremely 
thin and delicate young foliage needs normally a protection 
against the powerful chemical or thermal action of the 
sun’s rays, suggests that protection is afforded by the 
disposition of all the leaves in a vertical plane. 
A fuller discussion of this view will be entered into later ; 
it may, however, here be observed that the young secondary 
petioles are so flaccid that the leaflets borne by them hang 
vertically downward, no matter in what position the branch 
or the main petiole may be held ; so that the hanging of 
the branch would, on this view, seem superfluous. It is 
true that later these secondary petioles become more rigid ; 
but in the meantime the leaflets have become tougher and 
presumably therefore more capable of resisting any ill effects 
of exposure to direct sunlight. Treub, in a paper already 
quoted, seems also to see a means of protection in the 
pendent position. The rapid growth in length of the young 
branch and of the petioles of its leaves, has been already 
referred to ; but the physiological interest seems rather to 
centre in the check to this longitudinal growth — in the fact 
that several weeks after rapid growth in length has ceased 
it begins again. First the branch raises itself up ; then 
the petiole of the pinnate leaf is lifted up by means of a 
ventral pulvinar-like swelling ( polster ) at its point of attach- 
Journ. Linn. Soc., Vol. xxviii. 
