312 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



would offer little or no resistance to changes in form of the cell 

 within. The mother-cell then as soon as the mutual pressure of 

 other cells is removed, assumes the form of least surface, doubtless 

 due to cell-turgor and surface tension. 



It seems entirely probable that the cellulose wall of the typical 

 plant cell exerts much more opposition to changes in the form of 

 the protoplast, and has a restraining effect against an increase in 

 volume. But whether the typical cell-wall of plants has a high 

 or low degree of elasticity, we must conclude that these mother- 

 cells with their spherical form and loose arrangement in the pollen- 

 chamber are free to undergo such changes in volume and form as 

 their internal constitution will fa\w. The pollen-mother-cell 

 thus approaches the condition which-iaJoimd^in the egg cells of 

 many animals, and it is quite suggestive that we should here find a 

 mode of cell-division quite like t hat in the latter. Whether we 

 shall be able to explain this division in plantsoh the basis of surface 

 tension, as Robertson and McClendon have attempted in animal 

 cells, is perhaps a question. But it is clear that such factors as 

 surface tension, osmosis, and electrostatic equilibrium are in- 

 volved and their relation to the process must be considered. 



It may be that this close approach in the quadripartition of 

 pollen-mother-cells to the animal type of cell-division may throw 

 some light on the nature of the cell-plate. It is possible that in 

 all cell-divisions, animal and plant alike, there are fundamental 

 conditions tending to cell-plate formation, and that in the majority 

 of the cells of higher plants alone do we have the full complement 

 of factors necessary for the expression of these conditions in the 

 form of a visible structure. The ability of these pollen-mother- 

 cells to enlarge to a point of equilibrium between osmotic pressure 

 and surface tension may present conditions favorable for the 

 process of anatonose, as Errera termed it, in which soluble sub- 

 stances are formed in the equatorial plane. In the ordinary 

 tissue cells of the higher plants, the retentive cell-wall and adjacent 

 cells may make such enlargement impossible so that katatonose oc- 

 curs and a coagulation or precipitation of a compound organic salt, 

 takes place in the region of the equator. The relation of the spin- 

 dle fibers to cell-plate formation, and the relation of the former to 

 the nuclei, favors the idea that the cell-plate is primarily of nuclear 

 origin. It is not unthinkable (hat in all cases complex or simi)Ie 



