CYTOLOGY 37 



The fine polar striations have disappeared, and their 

 thickenings alone remain, and form the cell- wall, dividing 

 the two newly formed cells from each other. 



This, in a few words, is a simple account of the typical 

 process in this exceedingly complicated phenomenon. 

 Among the different tissue regions of various plants 

 considerable range of detail is found. It is a mere 

 outline of the marvellous process that is undergone 

 every time a cell is added to the body of the plant. One 

 of the most extraordinary and apparently one of the 

 most important features in this process is the fact that 

 the number of curved rods which range themselves 

 on the equator of the spindle is always constant for a 

 given species. For instance, there are twenty-four in 

 the Lily, fourteen in the Evening Primrose, and so on. 

 Though between each spindle formation the rods appear 

 to be completely lost, first in the long tangled thread 

 and then in the granular mass of the nucleus, each time 

 the process is repeated they appear in the same number, 

 and as they are ranged on the equator they split, so 

 that an equal number go to each pole and thus to each 

 of the newly formed nuclei resulting from the division. 

 The number of these rods varies in different species, but 

 it is seldom very large ; in some parasitic animals it is as 

 low as four. They are called technically chromosomes. 



One of the not least remarkable features of this whole 

 process is the fact that the stages described and illus- 

 trated above are found, not only universally in plants, 

 but also in animals. In their ultimate structure plants 

 and animals approximate closely, though in the kinds 

 of tissues formed by the aggregates of their cells, and 

 in their external features, they differ widely. 



Mention was made in the previous chapter of the 

 fusion which takes place between the male and female 



