f 



[ 133 ] 



IX. On the Growth and Composition of the Ovariv/m of Siphonodon celastrineus, Griffith, 

 especially with reference to the subject of its Placentation. By Joseph Dalton 

 Hooker, Esq., M.D., F.B.S. 8r L.S. (With a Plate, Tab. XXVI.) 



Read June 16th, 1857. 



IN a learned memoir upon some remarkable plants in the Hon. E.I.C.'s Botanic Gardens, 

 Calcutta*, Mr. Griffith established the genus Siphonodon upon a veiy curious Malacca 

 tree of doubtful affinity and singular structure, and accompanied his description with 

 many observations of the highest interest and importance to the student of structural 

 and morphological botany. Amongst these observations is one, which, though published 

 for now nearly fifteen years, has never attracted the attention of botanists, owing to the 

 limited circulation of the Calcutta Journal, but which, from its bearing on the subject of 

 placentation, has a peculiar interest to myself; for it appears to me to be, if correct, the 

 strongest proof hitherto adduced in favour of the theory which regards the placenta as 

 terminating the axis, and not as being referable to the carpellary leaf. To this theory my 

 own experience is opposed, and as I believed I had proofs of the invalidity of what ap- 

 peared to me to be the most cogent arguments previously adduced in favour of it, I more 

 particularly wished for an opportunity of testing the acciu'acy of Griffith's statement 

 with regard to Siphonodon. Mr. Griffith's conclusion is, " I beg to propose this plant to 

 botanists, as an instance in which the placenta is the termination of the axis, bearing 

 around its base a verticiUus of ovula, and produced upwards into a stigma, a single organ, 

 surrounded for the most part by a style with which it has no connexion." (loc. cit. p. 255.) 



The foundation for this proposition is Griffith's conviction that the ovules, of which 

 there are many in one horizontal series, are developed on an axis in the centre of the 

 flower, independently of the carpellary leaves, and not enclosed by them or by any other 

 organs except the perianth ; and that the subsequently developed carpellary leaves form 

 a verticOlus externally to the ovules, and rising upwards and inwards, finally enclose 

 them. These conclusions appear to me to be founded on erroneous observations, and the 

 chief object of the present communication is to lay before the Society my reasons for 

 supposing them to be so. 



I am indebted to my friend Dr. Thomson, who was weU-aware of the interest attached 

 to this plant, for specimens of Slpho7iodon flowers preserved in spirits, gathered from the 

 same tree, I believe, in the Hon. E.I.C.'s Botanic Gardens, which was described by Griffith. 

 These flowers are in aU stages of groAvth, from buds scarcely perceptible to the naked 

 eye, to fully expanded flowers, which measure about \ inch in diameter : I find, how- 

 ever (as is usual in flower-buds), that there is little relation between the size of the bud 

 and the development of its reproductive organs. In all, I invariably find both whorls of 

 the perianth to be fuUy formed in two closely imbricated series, before any traces of the 



* Calcutta Journal of Natural History, vol. iv. no. xiv. July 1843, p. 231, t. 14. 



