PROTECTION OF BUDS IN THE TROPICS. 351 
which is a drawing of a branch in a vertical position, shows 
the arrangement of the leaves, and how the leaf c is effectually 
shaded by the leaves a and b; and fig. 9, B, which is taken 
looking straight down upon the apex of another shoot, shows 
how effectually all the leaves younger than f are shaded aud 
protected, and at the same time how the leaf f receives a con- 
siderable amount of shade and therefore of protection. 
I investigated many species of Begonia growing wild, and 
always found the same result, namely, that the leaves were so 
arranged that the young leaves received a great deal of shade, 
and that the peculiar shape of the old leaf helped considerably 
in shading the younger leaves. 
We have now an explanation of the curious shape of the 
Begonia-leaves, viz. to take part in the protection of younger 
leaves; and although this peculiar shape may have some 
other function, yet at all events it is useful as an organ of 
protection. 
In many species grown in greenhouses in this country this 
arrangement is not clearly marked, the leaves being drawn to 
one side according to the prevailing direction of the light, while 
in its natural state the plant would be equally illuminated on all 
sides. 
4. Protection by Means of Gum. 
Treub, in the paper above quoted, mentions Tabernemontana 
and Lactaria as genera in which the buds are protected by means 
of a gummy secretion which covers over the growing-point, and 
to these we may add various species of Gardenia and Lasianthera 
apicalis, Thw. 
The case of Tabernemontana dichotoma, Roxb., is especially 
interesting. The buds of this plant are covered over with a gum | 
which does not completely harden, but remains in a semifluid 
condition; and as the leaves previously covered up grow and 
expand, the gum remains attached to their edges and stretches 
as a thin film between them; and so the next youngest leaves 
are for a certain time enclosed in a small four-sided chamber, 
two opposite sides of which are formed by two leaves, and the 
other two opposite sides by a thin film of gum. This gum is 
eventually ruptured and the same process is repeated. 
I had intended to have worked out completely the secretion of 
