404 IIOFMEISTER, ON 



In Juniper us and Thuja occidentals the phenomena of 

 cell-division are exactly the same as in the above-named 

 plants. In the former, however, on account of the small- 

 ness of all the parts, and in the latter, owing to the abun- 

 dance of starch- granules in the cell-contents, the obser- 

 vations are rendered much more difficult. 



In each special-mother-cell a pollen-cell is formed, which, 

 when its membrane first becomes visible, entirely fills the 

 cavity of the former. The two layers of the membrane of 

 the pollen-cell, the intine and the extine, are clearly distin- 

 guishable whilst the pollen-cell is still enclosed in the 

 special-mother-cells. The rudiments of the two hemi- 

 spherical appendages of the extine which are characteristic 

 of Abies pectinata, Picea vulgaris, and Pinus sglvestris, are 

 formed whilst the pollen-cell is still within the special- 

 mother-cell. These appendages consist, when in the young 

 state, of a soft inner substance, which passes on the outside 

 into a firmer cortical layer composed of reticulate ridge-like 

 protuberances. By the use of any fluid which attracts 

 water, such as a solution of sugar, the inner substance is 

 contracted into a smaller space, and the cortical layer of 

 that portion of the appendages which is furthest from the 

 middle point of the pollen-cell is made to turn inwards. 



After the pollen-cells have become free by the dissolution 

 of the walls of the mother- and special-mother-cells, a cell- 

 multiplication commences in them which is quite peculiar 

 to the gymnosperms, and is not seen in any other phseno- 

 gams. Two nuclei suddenly appear in the cell — a spherical 

 one, similar in all respects to the original nucleus of the 

 pollen-cell, and one somewhat smaller of a very flatly- 

 lenticular form (PL LIX, fig. 7). It is hardly a matter of 

 doubt that the latter is newly formed by the side of the 

 primary nucleus of the pollen-cell. Soon afterwards the 

 two nuclei appear separated by a membrane, convex towards 

 the larger one, having the form of a segment of a spherical 

 surface, and which divides the pollen-cell into two unequal 

 parts. That part which contains the flattened nucleus is 

 the smaller one. The disproportion in size of the two 

 parts is inconsiderable in Pinus Larix (PI. LIX, fig. 8), 

 but very remarkable in Picea vulgaris and Pinus sylvestris. 



