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



of this membrane in Clarkia I have but little doubt, and I 

 believe that it is also present in those species of Fuchsia 

 which I have mentioned as possessing a third tunic, as there 

 are in the pollen of these precisely the same appearances upon 

 which the opinion of its presence is founded in Clarkia elegans. 



The pollen granules of Saponaria viscida present, when 

 viewed through the medium of oil, a very remarkable appear- 

 ance, which I am only able to explain by supposing that it 

 depends upon some peculiar inversion or pitting of the ex- 

 tine. It conveys the idea of a membrane of a circular form, 

 smaller than the extine, being placed within it, and pollen 

 tubes to the number of ten escaping through apertures in it 

 and extending to the margin of the outer membrane. I refer 

 to this appearance here in the hope of directing the attention 

 of other observers to it, who may perhaps be able to afford 

 a more particular explanation of its nature. 



In the long axis of those granules to which the terms 

 cylindrical and elliptical are here applied, as well as of many 

 others, a line or furrow, as has been already remarked, is 

 noticed, concerning the nature of which various conjectures 

 have been hazarded, and none of which afford the true expla- 

 nation of the phenomenon. Malpighi compared granules of 

 pollen of this kind to grains of wheat, on one side of which a 

 furrow exists ; but this does not account for the furrow being 

 visible in every grain at the same time; Guillemin, attempt- 

 ing to account for the constant presence of the line, says that 

 it exists on both sides of the grain. He further supposes 

 this furrow to be a slit intended to facilitate the admission of 

 water into the interior of the granules, and the emission of 

 their contents ; neither is this explanation more satisfactory. 

 Fritzsche states it to be a thin part of the extine where the 

 sides of the pollen grain are contracted and meet, producing 

 the appearance of a furrow ; while Mr. Giraud regards this 

 line as a mere furrow in the extine which disappears on the 

 application of moisture, in which opinion Professor Graham 

 coincides * ; but neither of these gentlemen offer any expla- 

 nation either as to its origin or use. 



The true explanation of the nature of this furrow, about 

 which there are so many opinions, is, that it is a deficiency 

 in the external membrane of the pollen grain, intended to 

 facilitate the egress of the pollen tubes, one of which may be 

 distinctly seen to issue from each ; and the fact of its being 

 seen at the same moment in every grain of pollen is accounted 

 for by reference to the form of these granules. Those grains 



* See Ann. and Mag. of Nat. Hist, already referred to, and Prof. Graham's 

 Third Annual Report, read before the Botanical Society of Edinburgh, 

 March 1841. 



