1836.] Some remarks on the development of Pollen. 737 



Still I conceive it impossible to doubt the inherent mobility of these 

 granules. In some oily Pollens granules may be observed by the 

 sides of excessively minute drops of oil, certainly not exceeding the 

 larger granules twice in diameter ; and yet the granules will be seen in 

 active motion, and the oil perfectly stationary. M. Mohl contradicts 

 positively the curious fact advanced by M. Adolphe Brongniart, 

 that the granules are in some plants of the same size. Of this I cer- 

 tainly have never met with an instance. He likewise doubts the cur- 

 vature of some molecules ; but as Mr. Brown and M. Brongniart 

 speak positively on this point, I should prefer adopting their testimony. 



It is, likewise, said, that the idea of the granules nourishing the tubes 

 is untenable, and founded only on conjectures. But as it invariably 

 happens that the longer the tube is the fewer the granules are, this 

 opinion, which was I believe first indicated by the highest of all au- 

 thorities, Mr. Brown, cannot be said to be destitute of foundation. 



With regard to the development of Pollen, M. Mohl states that 

 his observations entirely confirm those of M. Brongniart, and that 

 the Pollen is formed from the granular matter contained in the cells of 

 the parenchymatous mass, which exists in each cell of the anther. 

 But although M. Brongniart certainly appears to have been the first 

 to have observed the formation of pollen by division, yet his account 

 in his " Memoire sur la generation et le developpement de l'embry- 

 on dans les vegetaux phanerogames," is certainly not characterised by 

 that precision which exists in the account of the development of the 

 Pollen in Tradescantia virginica by Mr. Brown, and subsequently in 

 that of Cucurbita Pepo by M. Mirbel. 



This latter, indeed, was the first instance examined by M. Brong- 

 niart, who states that what are now known to be lines of division 

 result from pressure. It still remains to be proved whether in any 

 instance the formation takes place, as M. Brongniart says it does, 

 in Cucurbita Pepo, by the cellules of the mass contained in the cavi- 

 ties of the anthers becoming directly grains of pollen. M. Mohl 

 mentions many instances in which the quaternary division is resorted 

 to ; it is owing to the continuance of the original adhesion that the 

 pollen of many plants is compound. The number, however, is not in 

 every case thus limited : the generality of the species of Mimosa, 

 Acacia, Inga, have pollen composed of sixteen cellules. But on the 

 development of these no direct observations have as yet been given. 

 The number of masses into which the originally simple nucleus may 

 be divided, is almost as frequently three as four. Of the binary com- 

 position of the mature Pollen Podostemon affords the only instance as 



