222 Parkin. — The Extra-floral Nectaries of Hevea brasiliensis 
is a simple epithelium, but on approaching maturity it becomes in places 
two or three layered (Fig. 7). Conspicuous nuclei and much cytoplasm 
without prominent vacuoles are present in the epithelial cells, as well as 
in the small cortical cells below. The cuticularized part of the outer 
wall is quite thick, as is shown in the drawing (Fig. 7 at). 
Examples of extra-floral nectaries with an epithelium divided in places 
are to be met with in Homalanthus populifera and Clerodendron Bungei 1 ; 
also a regularly two-layered epithelium exists in Prunus avium 2 . 
The diagram (Fig. 5) shows the position of the nectar-secreting epi- 
thelium in a transverse section of a typical median bud-scale ; while 
that of Fig. 6 represents the epithelium as restricted to the apex in the 
uppermost scale. 
The minute structure of the nectaries of the foliage leaves is similar 
to that of the scale ones. 
General Remarks. This case of Hevea brasiliensis is about the first 
example cited of bud-scales — cataphyllary leaves — serving as nectaries. 
The only other instance I have found at all comparable is that mentioned 
by Reinke 3 . He points out that the bud-scales, as well as the foliage 
leaves of Prunus avium, have glandular teeth which are honey-secreting. 
But here the transformation is very partial. The scales are not so 
modified as to be merely nectaries. Their primary function is still that 
of bud-protection. 
The Euphorbiaceae are rich in examples of plants with extra-floral 
nectaries. Baillon 4 , in his work on this natural order, enumerates the 
various types, showing that their situation may be various, such as on 
the stem, petiole or lamina ; and that different organs may be wholly 
transformed into them, such as stipules and leaflets. Hevea brasiliensis 
affords a still further type, viz. that of bud-scales serving as nectaries. 
Two or three questions suggest themselves as to the origin of these 
cataphyllary nectaries of Hevea. Are they connected by descent with 
the petiolar glands, or are they a fresh production of glandular tissue 
in the evolution of the plant ? What is the relationship between the 
non-nectariferous and nectariferous scales ? Have they been derived in- 
dependently at different periods from foliage leaves, or have the former 
arisen by further retrogression from the latter ? From an identity in 
structure between the petiolar and scale nectaries and from the situation 
of the glandular tissue in the uppermost scale it looks as if the two classes 
of nectaries were directly connected. The petiolar glands have perhaps 
become much more developed in the scales, so that the function of these 
latter is now wholly that of secreting honey. 
1 Morini, Contribute) all’ anatomia ed alia fisiologia dei Nettarii Estranuziali, Mem. Accad. 
Bologna, 1886, vii. 
a Reinke, Secretionsorgane, Prings. Jahrb., 1876, p. 125. 
3 Reinke, loc. cit. 4 Baillon, Etude gen^rale des Euphorbiees, p. 230. 
