308 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Study of Eqiiisetum and Isoetes, done at the same time as that on 

 Tropaeolum, and presenting the same evidence, which in the light 

 of the observations recorded above, must be regarded as doubtful. 



We are forced to conclude with Guignard then, as against Dippel, 

 Samuelsson, and others, that quadripartition and bipartition may 

 occur in either monocotyledons or dicotyledons. Furthermore, 

 there is no doubt that cell-plates occur in the bipartition of the 

 pollen-mother-cells as well as the vegetative cells in both mono- 

 cotyledons and dicotyledons. We have seen that the wall of the 

 pollen-mother-cell may be thickened in members of either one of 

 these groups. So that there seems to be no evidence that these 

 two groups of flowering plants differ in general in any way in 

 their mode of microspore formation. 



Since so little is known of the dynamics of cell-activities of 

 any kind it is very difScult even to attack the question as to 

 what physico-chemical processes are involved in cell-division. 

 However, it is to be hoped that the discovery of a closer relation 

 between the two diverse types of cell-division: that by furrowing, 

 characteristic chiefly of animal cells, and that by cell-plate, com- 

 mon to higher plants, will help to bring to view a new standpoint 

 from which the physiological processes of cell-division may be 

 more effectively studied. 



The almost infinite complexity of protoplasm has been so often 

 emphasized that it need not be further mentioned here. In 

 addition to the great variety of chemical compounds in the cell, 

 these exist in all sorts of physical states. There are' particles in 

 suspension, and substances in true solution; and between these 

 two extremes there are substances in all possible degrees of dis- 

 persity, including suspcnsoids and emulsoids, making up the col- 

 loidal mass of protoi)lasm. Not only is there an almost infinite 

 complexity, but the material is in a constant state of flux. 



In describing al)ove my observations on the migration of nuclei, 

 it was suggested that the nuclei move about in the mother-cell 

 as if they all bore electrical charges of like sign while the plasma 

 membrane bore charges of opposite sign. The location of elec- 

 trical charges on the membranes of the cell seems cjuite probable 

 from the standi)oint of recent developments in i)hysical chemistry. 

 According to tlie Gil)bs-Th()nis()n principle, there is a tendency 

 for substances to accumiilalc upon surfaces. It is practically 



