zooLoar and botany, microscopy^ etc. 85 



Ceratozamia longifolia and Zamia furfuracea among Cycadese, and in 

 Pinus Laricio, sylvestris, Pumilio, and Strohm, and Abies excelsa among 

 Coniferse. 



The pollen-grains of Cycadese divide either successively or 

 simultaneously ; both modes may occur in mother-cells from the same 

 anther. In the case of successive division, after the new nuclei have 

 been formed with their uniting-threads, and the cell-plate has already 

 become visible in these latter, corresponding to the plane of division, 

 the cellulose-ring makes its appearance as an externally projecting 

 cushion on the mother-cell. The starch-grains are grouped round 

 the new nuclei, especially on the side nearest the cell-plate. The 

 cellulose-ring projects at a later period into the cell, and meets 

 the cell-plate formed by thickening of the cell-wall. This ring had 

 been previously described by Juranyi and others as the young 

 division-wall. The stretched uniting-threads are by it constricted ; 

 and it is possible that the cell-plate takes part in the formation of 

 this ring. When it has attained a certain width, the new division is 

 suddenly formed at once from the cell-plate, and the division is 

 complete. The same process is then repeated in the daughter-cells, 

 except that the cellulose-ring does not attain so great a breadth and 

 thickness. In opposition to Treub, the author states that the division- 

 wall of the daughter- cells is formed entirely from the cell-plate. 



In the simultaneous mode of division the process is the same up 

 to the formation of the first cell-plate. The cellulose-ring is usually 

 smaller than in the first case ; when it has attained its full width, the 

 cell-plate is absorbed. The uniting-threads become afterwards 

 invisible, from the starch-grains becoming forced towards the first 

 division-plane, so that the space between the two nuclear spindles is 

 filled with them. They begin to disappear as soon as the halves of 

 the nuclear plate reach the pole of the nuclear spindle, a few only 

 remaining visible near the nuclei, the whole cell-cavity being 

 occupied by uniting-threads. The cell-plates are now formed, partly 

 between the nuclei, partly in the position of the first plate which has 

 disappeared, and the division is completed by the appearance of a 

 thin septum. After the thickening of the cell-walls, especially the 

 septa, the tetrads remain in this condition for a considerable time. 



The form of the pollen-grains and the mode of formation of their 

 membrane agree with those of some angiosperms (e. g. Allium odorum, 

 senescens, and nutans, and Tradescantia pilosa, &c.), and the author's 

 observations agree in essential points with those of Treub. The inner 

 layer of the wall of the mother-cell is always coloured by methyl- 

 green. In Ceratozamia longifolia the mother-cells have not the capacity 

 of swelling so strongly as in Zamia, and their membranes consist of 

 only two layers ; the inner one only, which becomes the wall of the 

 pollen-cell, is coloured by methyl-green. After this layer has become 

 detached from the outer layer of the cell-wall, an opening appears in 

 the latter, through which the young pollen-grains escape. The 

 membrane of the pollen-cell is therefore, as in other plants, the 

 innermost layer of the wall of the mother-cell. 



The process is the same in ConiferfB, except that the projections 



