RICHARDS: MITOSIS IN PODOPHYLLUM. 89 



in number from one to several — rarely more than four — and in 

 size and shape. In general they are irregular-spherical, but 

 may be compressed into different shapes. The variation in size, 

 which is considerable, depends on the age of the cell. As the 

 time for division approaches they grow smaller, finally disap- 

 pearing about the same time as the nuclear membrane. This 

 last fact sustains the conclusion that the nucleolus is simply a 

 storehouse for food material for the rest of the cell. 



In most cells up to the time of division there is noticeable a 

 peculiar vacuolated condition of the nucleus, and in these vac- 

 uoles lie the nucleoli. Figure 1 shows two such cells, one of 

 which has a single large nucleolus surrounded by a vacuole 

 and the other three. The term "vacuole" for the clear space 

 surrounding the nucleoli may be misleading. Experiments 

 seem to show that this colorless space contains something more 

 than a watery fluid, which is extracted by dehydration. By sub- 

 jecting the roots of Zea mays, Vicia faba, and other plants to 

 strong centrifugal force, Mottier ( i ) found that the nucleolus 

 with its surrounding clear space was thrown out of the nucleus 

 into the cytoplasm. "The nucleolus was still surrounded by the 

 space, a fact that seems to show that the colorless substance 

 has greater specific gravity than the other contents of the 

 nucleus. The colorless substance may represent the unor- 

 ganized nucleolar material." 



The cell wall of the resting cells stains much like the nuclear 

 membrane and is only slightly thicker. 



The cytoplasm stains fairly dark with iron hsematoxylin, 

 and shows its fine reticular structure quite plainly. Scattered 

 uniformly over the threads of the reticulum are large granules. 

 The cytoplasm of the cell stains slightly denser than the nuclear 

 sap. 



With regard to archoplasmic structures, not the slightest evi- 

 dence was seen to indicate that such structures as have been 

 described by Schaffner are ever present : /. e., centrosomes and 

 centrospheres. 



DIVIDING CELLS. 



The plane of division in these cells is mostly at right angles to 

 the axis of the root. This rule, however, is by no means in- 

 variable, for numerous cases have been found with the division 

 planes parallel to, or at an angle of forty-five degrees with, the 

 longitudinal axis (figs. 14, 20). 



