Linnaan Society. 



245 



bunda," in a letter from J. C. Bidwill, Esq., to Richard Taylor, Esq., 

 Under Sec. L.S. (See Ann. Nat. Hist. vol. viii. p. 438.) 



February 1, 1842. — The Bishop of Norwich, President, in the Chair. 



Read, " Contributions to Vegetable Embryology, from Observa- 

 tions on the Origin and Development of the Embryo in Tropceolum 

 majus." By Herbert Giraud, M.D., communicated by the Secretary. 



After referring to the researches of MM. Schleiden, Wydler, 

 Mirbel and Spach, and A. St. Hilaire, on this important point, Dr. 

 Giraud states that he was induced to select Tropaolum as the sub- 

 ject of his own observations on account of its solitary ovula, and 

 their comparatively large size, which render the individuals of this 

 family, as well as the allied Geraniaceee, peculiarly fitted for the pur- 

 pose. He arranges his observations under seven general heads cor- 

 responding with as many progressive periods in the growth of the 

 female organs, and extending from the completion of the anatropous 

 development of the ovule to the perfect formation cf the embryo ; 

 or from the commencement of the expansion of the bud to the com- 

 plete formation of the fruit. The results are collected from a great 

 number of dissections. 



In the/z>^ period, or just before the expansion of the bud, a lon- 

 gitudinal section of the carpellum from its dorsum towards the axis 

 of the pistillum, dividing the ovule, shows the latter to have com- 

 pleted its anatropous development. A portion of rather firm and 

 dense cellular tissue enclosing a bundle of vessels descends from the 

 placenta and in apposition with it to form the raphe, and terminates 

 in the base of the ovule. The nucleus has only one integument, at 

 the apex of which is the exostome or micropyle, opening close by 

 and to the outside of the point of attachment ; and the conducting 

 tissue of the style may be traced into the carpellary cavity as far as 

 the exostome. 



In the second period, during which the expansion of the bud and 

 the dehiscence of the anthers commence, and therefore before im- 

 pregnation, a small elliptical cavity makes its appearance near the 

 apex of the nucleus, having a delicate lining membrane formed by 

 the wails of the surrounding cells : this cavity is the embryo-sac, 

 and a minute canal may be traced leading from it to the exostome. 

 The apex of the embryo-sac encloses at this period a quantity of 

 organizable mucilage containing many minute bodies having the 

 appearance and character of cytoblasts. 



In the third period, the apex of the nucleus and of its integument 

 becomes slightly inclined towards the placenta. The embryo- sac is 

 much enlarged and lengthened ; its mucilage has disappeared and 

 given place to an elongated diaphanous utricle (utricule primordiale, 

 Mirbel ; vesicule embryonnaire, Meyen ; extremite anterieure du boyau 

 pollinique, Schleiden;) containing a quantity of globular matter or 

 cytoblasts. This primary utricle is developed wholly within the em- 

 bryo-sac, from which it is obviously distinct. 



The fourth period occurs after impregnation. The pollen tubes 

 do not extend into the carpellary cavity ; but the fovilla with its gra- 



