138 DR. J. D. HOOKER ON THE GROWTH AND COMPOSITION 



Before dismissing the subject of carpellary placentation, I would state that the other 

 arguments m favour of free axUe placentation, to which I have alluded at the beginning 

 of this communication, arc, the free central placenta of Frmiula, and the position of the 

 o'ST.ile of Tawios. I am not aware of any deviation from the free central placentation 

 having been observed in Frinmlaceae except by Prof. Henslow, who kindly placed ia my 

 hands for examination a monstrous flower of Prinmla vulgaris, in which two ovaria pre- 

 sented ovules developed on the confluent margins of some of the cai-peUary leaves, far 

 removed from the base of the ovary, and whoUy unconnected with the central placenta, 

 which stUl existed, but in a reduced form, and bore ovules. 



The other case is that of Taxus, adduced I believe originally by M. Sclileiden, who 

 considers the ovule as terminating the bracteate pedimcle or rachis which bears it. That 

 tills view is not tenable appears to me to be proved by the fact that I have found two and 

 even three ovules at the apparent apex of the peduncle. I fm*ther cannot but consider 

 the bracteate peduncle of the female flower of Taxus* as a genuine cone, the majority of 

 the bracteae of which bear no ovarian scale and ovule. When more than two ovules are 

 developed in this cone, these almost invariably wither and disappear at a very early 

 period ; but I have examined partially diseased cones of Taxus, in which the second ovule 

 had enlarged and persisted in a scale below the terminal one. 



"With such a preponderating mass of evidence in favour of carpeUary placentation, 

 derived from the normal condition of both simple and compound pistiUa, in which the 

 relation of the parts cannot be misinterpreted, and from monstrous states of ovaries whose 

 composition is more obscure, it does seem to me unpliilosophical to call for the operation 

 of a second law to explain the comparatively few exceptional examples of placentation 

 that are not at once referable to the carpeUary. Of these exceptional cases, Frimiulacece, 

 Caryophyllece, and their immediate allies have always been supposed to be the most 

 difficult to explain away, but Caryophyllece, both in theii- normal state and as monsters, 

 present many cases of carpeUary placentation, and Professor Henslow's Frinmla demands 

 a double law for one flower, if the free axile placentation be not considered a modification 

 of the carpeUary. 



If it be admitted that the floral whorls are formed from leaves, even when appearances 



a leaf in the earliest stage of its deTelopment. A contraction below the gland separates it from the lamina of the leaf, 

 which is independently developed with a convolute vernation. 



While upon this subject, 1 may further mention, that the bilobed lamina of Dioncea is unquestionably the true 

 lamina of the leaf of that plant ; and that it is iuflexed in early vernation, as in Drosera, to which it is so closely 

 allied, and to which it is further united by means of Aldrovandra. 



Of Aldrovandra I may remark, that this very rare and singular plant has been rediscovered by Dr. Thomson in the 

 immediate vicinity of Calcutta. It was originally found there by Dr. Roxburgh, but unsuccessfully sought for by 

 Dr. Wallich, Griffith, Voigt, and indeed every Calcutta botanist. Though unknown in any intermediate spot between 

 Europe and Calcutta, I can find no difference whatsoever amongst the specimens from these widely-sundered localities. 



* The fleshy cup of Taxus, which is usually called a disk in botanical works, but which is regarded as an arillus by 

 Schleiden, is undoubtedly the outer coat (primine) of the ovule ; it is developed at an early stage as an annulus in 

 immediate contiguity with the second coat (secundine) : this second coat in Taxus, as in many other Conifers, becomes 

 the outermost covering of the seed, or tegmen. I have ventured to allude to this here, as I am not aware that the 

 true nature of the integuments of the seed and ovule of Coniferce has been correctly stated in any general systematic 

 work. 



