19 



Minute granulated microsomes appear at points along 

 these fibrils in the mid-region of the cell forming the ceil- 

 plate, and are gradually formed into a partition wall which 

 divides the two daughter cells (Fig. 29). NucleoH reappear 

 usually in the polar regions of the daughter cells, a nuclear 

 membrane is formed, and the resting nucleus is completed 



This brief account of mitosis is of general import only 

 and not descriptive of what may take place in any 

 particular plant, but includes phases observed in several. 



AMITOSTS 



is another form of nuclear division known as direct, where 

 the nucleus separates into two parts, each of which either 

 goes to form the nucleus of a new cell or the old cell 

 becomes binucleate, and if the process be repeated, multi- 

 nucleate (Fig. 30). This mode, at first thought to be of 

 almost universal occurrence, was, after the discovery of 

 mitosis, first described by Anton Schneider in 1873, found 

 to be of limited application, at least in cells of the higher 

 plants. It is chiefly observed in cells in apparently 

 abnormal physiological conditions and others too old for the 

 ordinary stages of mitosis to take place as many large cells 

 of vegetative tissues, and is also commonly seen in the 

 large cells surrounding developing sporogenous cells and 

 spores, e.g., the tapetum of anthers and sporangia of higher 

 cryptogams (Fig. 31). 



The process begins with a median constriction 

 in the nucleus, which gradually deepens until 

 the division is complete, and the daughter nuclei 

 usually remain in close proximity to each other. 

 There is no division of the cytoplasm, except in 

 those cases where walls are formed, the cells simply 

 becoming multinucleate. In some instances there may be 



