Mr. Hassall on the Structure of the Pollen Granule. 97 



of pollen to which the term cylmdrical is applied, are, as 

 has been already noticed, more or less of a triangular or 

 trilobate form, and at each angle, or between each lobe, a 

 furrow exists ; so that, as each granule, from its shape, must 

 rest upon one or other of its sides, one angle and one line 

 will necessarily be presented to the eye of the observer. But 

 another explanation is requisite to account for its constant 

 presence in those granules to which the term elliptical is as- 

 signed ; these, though of an elongated form, like the others, 

 are rounded in their short axes, except on one side, ^vhich is 

 slightly flattened and indented. In this indenture the single 

 furrow possessed by these granules is placed ; hence it results 

 that each must rest either on its flattened surface, with the 

 furrow looking downwards, as most frequently happens, in 

 which case it will still be apparent through the body of the 

 granule, owing to^ its transparency; or it will fall on the 

 rounded surface opposite the furrow, which now looks di- 

 rectly upwards. Thus, in whichever way the grain rests, the 

 furrow ^vill still be apparent. Should it alight upon its side 

 it will not remain in this position, but will roll over to the 

 convex surface, which constitutes its centre of gravity*. 



The pollen grain of Criniim amabile is flattened and broad 

 on two surfaces, differing in this particular from the pollen of 

 all other Amarijllidacece which I have examined, down each 

 of which a furrow is placed ; and from this form also it fol- 

 lows that one line will ever be opposed to view, as the granules 

 rest upon one of their broad surfaces. And again in Citrus 

 aurantium, Ranunculus acris and Rubus fruticosus, the gra- 

 nules are somewhat elongated, and consist o^ four lobes, be- 

 tween w hich the fissures are placed ; and as they most gene- 

 rally lie on two of the lobes, the other two, with a fissure be- 

 tween them, will, as a matter of course, be turned upwai'ds. 



Lastly, many kinds of pollen, as o^the Poly (/ake, Crucianellce, 

 Labiatce, &c., are furnished with a number of furrows, some of 

 which, in all postures, will be visible. A careful examination 

 of the pollen granules of Convolvulus arvensis, Lillum longi- 

 florum, Crinum amabile, and Ranwiculus acris, will convince 

 any one of the correctness of this explanation ; both of the 

 nature of these lines, and of the reasons for their invariable 

 appearance in each granule at the same moment. 



In most elliptical pollen, covering each of the fissures, an 

 oval piece of membrane is to be observed, the use of which I 

 conceive to be to prevent the pollen tubes from escaping too 



* Malpighi's comparison ofgi-anules of tliis foi-m to grains of wheat is by 

 no means inapt, bnt still withont the above explanation it is incomplete, in- 

 asmuch as it does not account i'oY the constant appearance of the furrow. 



Ann. ^- Mar/. N. Hist. Vol. viii. H 



