of the Structure of the Pollen Granule. 95 



grains for cells." This idea of Mohl's is supported principally 

 by reference to the fact, that in some pollen — for example, in 

 that of Pitcairnia latifolia — manifest transitions from one of 

 these formations to the other, that is, from the cellular to the 

 granular, may be detected. This explanation is probably the 

 right one. 



" A question difficult to resolve is, to know if one might 

 still admit the existence of very small cells, when the external 

 membrane appears to be no more formed of large grains, but 

 presents a smooth surface with very little points (or spots), 

 cases without comparison more frequent than that of the true 

 cellular formation of the external membrane. The solution 

 of this question is allied to the clearing up of some points of 

 vegetable anatomy still very obscure, and which have not suf- 

 ficiently fixed the attention ; I mean to the exact knowledge 

 of the structure of those cryptogamous plants among which 

 first begin to appear certain rudiments of cells in the gelati- 

 nous mass which forms them, under the form of little grains,, 

 for example, Ulva, Palmella, Hydrurus, Batrachiospermum, 

 Myurus, &c, and afterwards to the inquiry of the manner in 

 which the cells are united to each other in plants of higher 

 development." 



" A detailed examination of these points," continues Mohl, 

 ce would delay us too long ; we pass on then to observe, that 

 the gelatinous material, which forms by far the greater part 

 of the bulk of these Cryptogams, corresponds to an element re- 

 duced almost to nothing in more elevated plants, which is found 

 between the cells and produces their reciprocal union, but 

 whose anatomical examination is only possible in a small num- 

 ber of vascular plants, and that the little scattered grains ought 

 to be considered as the analogues and first rudiments of cells. 

 Such is likewise, according to me, the organic constitution of 

 the [granular or] dotted external membrane ; it is then formed 

 of two elements: 1st, of small grains of a cellular nature; 

 2nd, of a uniform material of a gelatinous nature which unites 

 these grains into a membrane. Not only is this view sup- 

 ported by the accordance which this granular membrane 

 offers with the constitution of the plants of which I have 

 spoken, but there are direct observations which are in its fa- 

 vour. One circumstance which speaks for the analogy of the 

 grains with the cells is, that in the grains of pollen whose 

 external membrane is of a granular nature, as well as in 

 those which are provided with a membrane distinctly cellular 

 the oily substance, coloured, is formed and preserved in this 

 external membrane. Another fact, which is still further fa- 

 vourable to this view, is the series of modifications by which 



