736 Some remarks on the development of Pollen. [Nov. 



objected, that there is no proof of the universal necessity of the appli- 

 cation of the tube to the foramen, or that portion of the ovulum cor- 

 responding to this. Still there is ample proof of this necessity in 

 Asclepiadese ; and, as I have observed it in Solanea, Gentianece, 

 Nelumborea, and Legnminosa, I have no doubt that tbe application of 

 the tube to the foramen is absolutely necessary to insure fecundation. 

 And with regard to the length produced by the action of water, I have 

 seen tubes produced from the grains of Pollen in a species of Impa- 

 tiens, I believe the Impatiens tripetata of Roxburgh, exceeding six or 

 eight times the long diameter of the grain ; these tubes, however, 

 never even after protracted immersion contained any granules. Their 

 growth in the above instance may be actually watched, the apex of 

 the tube creeping along with an excessively slow vermicular motion. 



M. Mohl states, that Asclepiadece alone have no outer membrane. 

 The existence of this membrane as a distinct integument has been 

 proved by Mr. Brown ; although in almost all the species of this 

 family, the outer coats are in a state of mutual adhesion*. 



Conifera are said to have three coats ; the intermediate one resem- 

 bling the inner membrane of ordinary Pollen, especially in its great 

 extensibility ; in this property the innermost, although it has the ordi- 

 nary structure of inner membranes of other Pollens, is deficient. 



As I have mentioned before, this author considers the outer mem- 

 brane as the secretory one, and he denies the possession of secretory 

 powers by the papilla? ; an opinion stated to be advanced by Mr. 

 Brown. M. Mohl proves that the secretion of oil is not limited to 

 any papillosity of surface ; of this Pardanthus Chinensis is an instance. 



This botanist doubts the proper activity of the molecules or granules 

 contained in the fovilla, and he adduces the authority of M. Fraun- 

 hofer as to the utter impossibility of preventing currents in liquids. 



* I find that the cells of the anther of Oxystelma esculentum are at an ex- 

 tremely early period lined by a free simple sac containing irregular masses of 

 opaque granular matter ; soon after, this cell appears to be filled entirely with 

 the granular matter, by which it is rendered somewhat turgid. In this state it 

 is detachable with extreme difficulty. When the flower bud is two lines long, the 

 mass has become cellular, and the granular matter correspondingly subdivided. 

 The subsequent changes consist merely in the increase of size and consistency 

 of the parts, and perhaps in the development of the inner membrane. We may 

 hence be allowed to infer that the mass, from which all Pollen grains seem to 

 be developed, is in Asclepiadece reduced to a single cell : and that the grains 

 are produced by its indefinite division. The only material objection to this view 

 exists in the original cell itself entering into the composition of the grains of 

 Pollen ; and in its not disappearing, as appears to be generally the case. 



