32. Mr Gardiner, On Hodgsonia heteroclita. [ Nov. 8, 
bracts, since they are associated with the rudimentary flower bud. 
They are doubtless identical with the similarly modified bracts 
which occur in connection with the fully developed flowers. The 
glands are found on the lower surface of the bract and belong to 
the same type as those of Luffa, although of a distinctly higher 
order. Glands of a similar nature also occur on the under surface 
of the foliage leaves and on the sepals. The substance secreted 
by the glands is most probably of the nature of nectar, and the 
whole structures are to be regarded as extra-floral nectaries. 
Having shortly described their histology, the author proceeded to 
make some remarks upon their function. A careful survey of the 
various gland-bearing genera of the Cucurbitaceae and Passi- 
floraceae, and a comparison of such cases as those presented by 
Passiflora quadrangularis and Passiflora foetida, placed it, in his 
opinion, beyond doubt that the function of the extra-floral nectaries 
of the two orders is to attract certain insects—probably ants— 
which are of service to the plant in protecting it from the attacks 
of other and harmful insects, such as caterpillars, which are 
accustomed to creep up the narrow stem for the purpose of devour- 
ing or otherwise injuring the young growing shoots. 
As regards the fertilisation of Hodgsonia, the author showed 
that there were special contrivances to prevent the animal which 
fed upon the nectar of the flower from obtaining that of the extra- 
floral nectaries, and wice versa, and stated that considering all the 
circumstances of the case it was exceedingly probable that fertili- 
sation was accomplished through the agency of a large night- 
flying moth. 
November 22, 1886. 
Mr TROTTER, PRESIDENT, IN THE CHAIR. 
The following communications were made to the Society. 
(1) Note de Géométrie cinématique. Par le Professeur 
A. Mannheim. 
Dans son Traité des flucions, Maclaurin a fait connaitre une 
élégante construction du centre de courbure de la développée d’une 
ellipse. Je retrouverai cette construction a la fin de ce travail en 
la déduisant d’une autre 4 laquelle j’arrive par l’application de 
quelques propositions de Géométrie cinématique. 
