350 MR. M. C. POTTER ON THE 
same relative positions, and so protect other young leaves, and 
so on. 
Galactodendron utile affords also an example of this mode of 
protection, the young and tender leaves being protected by 
older ones; and further protection is also gained by the tender 
leaves assuming a vertical position until sufficiently strong to 
resist the atmospheric conditions. 
GOSSYPIUM. 
' Another very interesting case of older leaves protecting the 
younger ones is found in the various species of the genus Gos- 
sypium. In this genus the leaves are cordate, with rather long 
petioles, which, for some time after the leaf has expanded, 
assume a position only slightly inclined from the vertical: the 
lamina forms an acute angle with the petiole, and is so arranged 
that in the young condition it hangs nearly vertically (Pl. XLVII. 
fig. 8, A, b) downwards ; thus the lamina of each leaf makes an 
acute angle with the axis of the branch on which it is borne. 
In this way each leaf, in its turn, stands nearly over the actual 
growing-point (fig. 8, B and C), and shades all leaves younger 
than itself; and here we see the advantage which these plants 
gain from the cordate base of their leaves, namely, that the 
lamina being continued backward is able more effectually to 
shade the growing-point. The manner in which the growing- 
point can be shaded is seen in fig. 8, B and C, which are taken 
from photographs of living plants in which the camera was placed 
directly over the shoot. In fig.S, B, the young leaf b is partially 
seen; but all leaves younger than b and the growing-point are 
invisible, and hence completely shaded ; and in fig. 8, C, the leaf 
a entirely shades the growing-point. 
BEGONIA. 
A still more interesting case of this kind of protection is 
found in the genus Begonia. The leaf of the Begonias, it is well 
known, is unsymmetrical (Pl. XLVIII. fig. 9, A), the want of sym- 
metry being caused by the base of the lamina being semicordate ; 
one side of the base is largely developed, while the other side 
remains almost undeveloped. Just asin the case of Gossypium 
previously described, the leaves are so arranged that the lamina 
of the older leaves shades over the younger ones. Fig. 9, C, 
