THE POLLINATION OF SATYRIUM BICALLOSUM , THUNB. 153 
at the apex of the spur was shedding its cuticle, and below this, the epidermal 
cells were secreting a sugary liquid. In a still older flower, the spurs were more 
than half filled with honey, and the few hairs remaining had their cell contents 
disintegrated. The cuticle had become entirely detached from the epidermis. 
Secretion of honey, in this species is sub-cuticular, and occurs after the flowers 
have opened. Honey is most abundant in the lower flowers of a spike, i.e., in 
those flowers in which the stigmatic surfaces are receptive. It thus appears 
that the spurs of Satyrium bicallosum remain throughout the life of the flower 
in a condition comparable to that found only in newly opened flowers of 
S. coriifolium. It will be remembered that Darwin 1 found no free honey in 
the spurs of Orchis mono, 0. maculata and 0. pyramidalis, and concluded that 
the visiting insects penetrate the membranes lining the spur, in order to obtain 
the sugary juice beneath. 
During the daytime, the flies concerned in the pollination of S. bicallosum 
are not frequently seen, but at dusk they appear in large numbers, and fly 
fairly actively. It seems probable that cross-pollination takes place most 
frequently at nightfall, and that once a fly has a pollinium attached, it does 
not usually again take flight, but runs from flower to flower, and from in- 
florescence to inflorescence. Almost all flowers from the lower part of the 
spike have both pollinia removed after the flower has been open for a night, 
and, as the plants set seed abundantly, cross-pollination must be very effectively 
carried out. 
I saw no other insect visitors, though aphides are occasionally seen at the 
bases of the ovaries; they play no part in pollination. 
Members of the genus Satyrium are fairly abundant in the south-western 
district of South Africa, but, although some species are so common, practically 
nothing is known as to their mode of pollination. From their structure and 
colouration, S. pumilum, Thunb. and S. saxicolum, Bolus, would appear to be 
particularly interesting types; while the very remarkable structure of the 
column in S. rhynchanthum, Bolus would w r ell repay further study. It is to be 
hoped that those in a position to carry out field observations will continue this 
work. 
BIBLIOGRAPHY. 
Bolus, H., 1918. The Orchids of the Cape Peninsula. 
Darwin, C., 1904 . The various contrivances by which orchids arc fertilised by insects. 
(Second edition.) 
Marloth, R., 1895. Trans. S. African Phil. Soc., vm. Minutes of Proc., Feb. and Mar. 
1915. The Flora of South Africa, vol. iv. 
Trimen, R., 1864. On the Fertilisation of Dim grandiflora, Linn. Jour. Linn. Soc. Bot. VII, 
pp. 144-147. . 
• 1867. On the Structure of Bonatea -speciosa, Linn, sp., with reference to its fertilisa- 
i tion. Jour. Linn. Soc. Bot. ix, pp. 156-160. 
1 Darwin, 1904. 
