156 ORGANOGRAPHY. BOOK I. 



escens, they were observed by Guillemin to be nearly square ; 

 in Lavatera aeerifolia to be oval, much attenuated to each end. 

 In Qilnothera they are triangular, with the angles so much 

 dilated as to give the sides a curved form. In Jacaranda 

 tomentosa I have remarked them to be spherical, with three 

 projecting ribs tapering to either apex. In the Cichoraceae of 

 Jussieu the granules are spherical with facettes ; in Dipsaceae 

 they are a depressed polyedron ; in Scabiosa caucasica patelli- 

 form and angular. (For other modifications see Plate IV. 

 fig. 12. to 37.) 



Little lids are perceptible in some kinds, opening to admit 

 of the passage of pollen tubes. Fritzche describes one in 

 Grasses, two in the Nettle, four in the Orange, and six in the 

 Primrose. Purkinje remarked three in the Passion Flower. 



In most spherical or elliptical pollen, with a smooth surface, 

 a line is observable along the axes of the granules, when they 

 are dry, which disappears upon the application of moisture. 

 This was long ago remarked by Malpighi, who compared 

 granules of pollen of this kind to grains of wheat, one side of 

 which is convex and the other furrowed. Guillemin is of 

 opinion that this supposed furrow exists on both sides of a 

 grain of pollen, because, let there be never so many of this 

 description examined at the same instant, the appearance will 

 be visible in all. But it is probable that the strong trans- 

 mitted light which is used in microscopical examinations of 

 minute objects would render the furrow visible on both sides 

 of a grain, although it really existed only on one. 



As to the nature of this supposed furrow, nothing positive 

 is known. Guillemin supposes it to be a slit intended to 

 facilitate the admission of water into the interior of the gra- 

 nules and the emission of their fovilla, and he further com- 

 pares it to the line of dehiscence of each lobe of the anther. 



Fritzche states it to be a thin part of the membrane, where 

 the sides of the pollen grain are contracted and meet, pro- 

 ducing the appearance of a furrow. 



Many botanists are of opinion that the coat of the pollen is 

 a simple cellular substance ; others think it a solid membrane ; 

 and a third class of writers insist upon its consisting of two 

 integuments, the outer of which is cellular, the inner mem- 



