224 Parkin . — The Extra-floral Nectaries of Hevea brasiliensis 
they represent probably the middle leaves of the primitive shoot, the 
lowest having ceased to act as foliage leaves. 
The reason why in an ordinary shoot such as that of the Beech the 
middle leaves should generally be the largest is perhaps owing to the 
intensity of growth during development, first rising gradually to a maximum, 
then falling again till growth ceases. This would result in the first and last 
formed leaf-blades being the smallest. 
The only other species of Hevea I have been able to examine is 
H. sprnceana , Mull.-Arg., a very closely allied one. It possesses similar 
nectariferous scales. 
Summary. 
1. Hevea brasiliensis possesses two kinds of extra-floral nectaries : — 
(a) Small inconspicuous glands situated on the upper surface of the 
foliage leaves, where the three leaflets join the petiole (Fig. 3 n). 
(b) Large conspicuous glands borne on vestigial foliar structures — 
4 bud-scales 7 — which are situated on the shoot below the foliage leaves 
proper (Figs. 1 and 2 ns). 
2. The ■ bud-scale 5 nectaries are a prominent feature of the young 
expanding shoot, and are functional till the foliage leaves are mature, when 
they wither and drop off. They are present in saplings, as well as in adult 
trees, but were not observed in seedlings. 
3. Besides these nectariferous structures, one or more insignificant bud- 
scales without nectaries may be present at the base of the shoot (Figs. 
1 and 2 .s'). 
4. The minute structure of the foliar and ‘ bud-scale ’ nectaries is the 
same. Each consists of a well-defined secretory epithelium with a thick 
cuticle. The original cells of this epithelium may be divided here and 
there by one or two tangential walls to form in places a two- or three- 
layered epidermis (Fig. 7). The nectar escapes by the bursting of the 
cuticle. 
5. The two kinds of extra-floral nectaries are considered as homo- 
logous ; that is to say, the ‘ bud-scale ’ one may be regarded as a further 
development of what was at one time a petiolar nectary. 
6. These nectariferous structures, occupying relatively the same 
position on the shoot as ordinary bud-scales, probably never had a 
protective function, but have been derived directly from what were once 
foliage leaves by the disappearance of the lamina and an increase in size 
of the nectary. 
7. According to the usual view taken of the function of extra-floral 
nectaries, the ‘bud-scale’ glands may be looked upon as attracting ants to 
keep off insects injurious to the developing foliage. As soon as the foliage 
