On the development of the Spores of Anthoceros Icevis. 79 



are produced three or four in number from the interior of 

 other cellules. 



He gives no detail of the manner by which this is per- 

 formed, but he exposes, in the most detailed manner, the 

 analogous fact, the development of the pollenic grains, espe- 

 cially those of the Citrouille. 



In this case the membrane of the cellules in which the 

 pollenic grains are found, and which is full of a granular 

 mucilaginous substance, becomes gorged with juice, and swol- 

 len to such a degree that it assumes a considerable thick- 

 ness ; on its internal surfaces there are four septa produced, 

 which direct themselves toward the centre of the cellule, 

 and divide its contents into four parts, and uniting in the 

 centre of the cellule in such a manner that the cellular ca- 

 vity is divided into four compartments entirely separated. 

 Then there is formed in each of those compartments, and 

 around the granular substance which it contains, a mem- 

 brane which in the Citrouille is at first smooth and colour- 

 less, afterward becomes yellowish, and covered with papillae 

 (mamelons). Examination of ripe grain exhibits that inter- 

 nally to this membrane there is formed another, which at 

 certain points is found joined to the external membrane. 

 The cellules in which the pollenic grains are formed become 

 dried and tear, so as to liberate those pollenic grains. 



In a later Memoire (Ann. Sc. Nat. 2d ser. iv.) M. de 

 Mirbel enters into details concerning the formation of these 

 two membranes, the one external, and the other inter- 

 nal, and indicates that they draw their origin from the 

 cambium contained in the mother-cellules of the pollenic 

 grains, that is to say, from the mucilaginous mass which 

 before the formation of the membrane of the pollen enve- 

 lopes the pollenic grains, and which fills the space between 

 these grains and the wall of the mother-cellule, and which 

 first becomes changed into the external membrane of the 

 pollen, and afterwards into the internal membrane. 



