The Microscope. 227 



other. The nuclei are small and not easily seen in the living 

 cell, but fixing with 1 per cent, chromic acid, and staining with 

 carmine will show them distinctly. They are not often found 

 in division and are too small to be satisfactorily studied, so they 

 will not be considered further here, and we will confine our atten- 

 tion to the division of the cell only. 



The young division-wall is first evident as a delicate ring run- 

 ning around the inner surface of the cell-wall, and this rapidly 

 grows inward pushing the protoplasmic cell-body inward until 

 finally the ring closes up completely and forms a thin membrane 

 completely across the cell, cutting the protoplasm completely in 

 two (Figs. 2-6.) The process occupies between three and four 

 hours under ordinary circumstances, and may be readily fol- 

 lowed. 



In the common pond-scums of the genus Spirogyra (Fig. 8) 

 and in many Desmids (Fig. 9. ), the cell divides in much the 

 same way as in Cladophora, but here the single nucleus divides 

 simultaneously with the cell. In all the common Spirogyras 

 the division takes place normally at night, and in order to follow 

 it successfully the process must be checked. This can be done 

 by keeping the plants in a warm room until nearly the time 

 for division to begin (about 11 P. M.), and then lowering the 

 temperature to near the freezing point. When the temperature 

 is nearly freezing out of doors, this can of course, be done by 

 simply placing the vessel containing the plants, outside. On 

 bringing the plants thus treated into the laboratory, division will 

 begin almost immediately. 



After undergoing several preliminary changes, similar to those 

 to be described further on, the nucleus divides into two similar 

 portions which quickly separate and soon assume the form of the 

 original nucleus. They remain connected for some time by deli- 

 cate threads which disappear about the time the division-wall is 

 xjomplete. 



While a good general idea of the processes of cell-division may 

 be had by a study of the lower plants, for understanding the 

 minuter details we must choose subjects from among the higher 

 plants, and while in a few cases we can follow through the pro- 

 •cess in the living cell, it is usually necessary to have recourse to 

 fixing and staining agents in order to obtain the best results. 



Among the flowering plants the mono-cotyledons are on the 



