Mr. H assail on the Structure of the Pollen Granule. 93 



XI. - A Critical Examination of MohVs Views of the Gene- 

 ral Structure of the Pollen Granule. By Arthur Hill 

 Hassall, Esq., M.R.C.S.L., Corresponding Member of 

 the Dublin Natural History Society. 



Mohl considers the external membrane of the pollen granule 

 to be the secreting organ of the oily liquid found upon all pol- 

 len, but more abundantly upon such as is either cellular or 

 spinous, and that it is this liquid which determines the colour 

 as well as the viscosity of the pollen. 



In the remarks 1 have already published upon the pollen 

 granule*, I have suggested the probability that this viscid 

 fluid, which differs so much from the fovilla in appearance, is 

 derived from the cell in which the pollen is originally deve- 

 loped ; and this suggestion appears to gather some degree of 

 confirmation from the fact of its being met with in greater 

 quantity upon pollen which has just escaped from the anther. 



This external membrane Mohl states to vary considerably 

 in intimate structure according to the plants . in which it is 

 examined, being either cellular or granular, and but rarely, if 

 ever, perfectly homogeneous. "The cellular structure," he 

 observes, " without being rare, occurs but in a small number 

 of plants. It is met with as frequently among Monocotyle- 

 dons as among Dicotyledons. It is not a character of a fa- 

 mily ; on the contrary, this structure is observed in genera of 

 the same family, or in species of a genus, while allied plants 

 present another." My opinion upon this point is, that it 

 most frequently, if not invariably, is to be relied on as afford- 

 ing a character of at least generic importance, and that it is 

 not uncommonly of higher value, running through several 

 contiguous genera. The cellules are more or less regularly 

 six- or seven-sided, and of various sizes. The network formed 

 by their union has been mistaken by some observers for the 

 ramifications of vessels in the external membrane of the pol- 

 len granule, " an error similar to that which had place relative 

 to the epidermis of leaves." 66 In all cases where the external 

 membrane is cellular," Mohl goes on to remark, " I have found 

 the surface of the granule smooth and destitute of spines." 

 "This result is in truth altogether opposed to that M. Bron- 

 gniart announces, who believes to have found in the centre of 

 each cell an excretory conduit under the form either of a hair 

 or a spine ; for example, in Mirabilis Jalapa, Ipomcea purpu- 

 rea ; but my observations have informed me, that all the spe- 

 cies of pollen described by M. Brongniart as cellular and spi- 



* See Annals and Magazine of Natural History for Oct. last, vol. viii. p. 92. 



