354 DEVELOPMENT OF POLLEN MOHL. [BOOK i. 



thick and succulent wall of each pollen-cell dilated, so as to 

 leave a void between its inner face and the granules, not one 

 of which separated from the mass, which proved that a force 

 of some kind held them together. Shortly after four append- 

 ages, like knife-blades, developed at equal distances on the 

 inner face of the pollen-cell, and gradually directed their 

 edge towards the centre, so that they began by cleaving the 

 granular mass in four different lines, and finished by dividing 

 it into four little triangular masses ; and when the appendages 

 met in the centre they grew together, and divided the cavity 

 of the pollen-cell into four distinct cavities, which soon after 

 rounded off their angles, and in a short time the little granu- 

 lar masses became spherical, like melted lead run into the 

 hollow of a bullet-mould. The partition of the mass thus 

 brought about by the appendages seems to me to indicate 

 that at this period the mass was not protected by a special 

 integument, and that the mutual adhesion of the granules 

 was very weak. 



" When things had arrived at this point, the portion of the 

 tissue formed by the pollen-cells separated itself from the 

 surrounding parts, and each pollen-cell became loose, gene- 

 rally in the form of a square parallelepiped with rounded 

 angles ; each little mass of granules gained a smooth, colour- 

 less, transparent membrane, which was at first membranous, 

 but afterwards became thick and succulent, and soon began 

 to take on the characters peculiar to the pollen of the Gourd. 

 The integument began to bristle with fine conical papillae; 

 several roundish lids were traced out here and there on its sur- 

 face; it hardened, became opaque, assumed a yellow colour, 

 ceased to grow, and attained its perfect maturity." Mirbel 

 adds to this highly interesting statement, that he finds in the 

 generality of plants that the mode of forming the pollen is 

 much the same as in the Gourd. 



Observations upon the same subject by Professor Mohl 

 were published in Berne, in 1834. The principal points of 

 novelty in regard to the development of the pollen are, that, 

 1. The union of pollen-grains in fours is sometimes perma- 

 nent, sometimes very temporary. 2. That the four are 

 sometimes placed upon the same plane, sometimes in the 



