PROTOPLASM AND PLANT-OBLLS. 11 



plasmic spindle; [d) the chromosomes split longitudinally, 

 and the daughter-fibrils move along the kinoplasmic spin- 

 dle to the centrospheres (which have divided) where they 

 form the polar disks (Fig. 6, G) ; (e) the polar disks gradu- 

 ally assume the form of tangled fibres of the new nuclei. 

 When these changes are nearly completed the cytoplasm 

 divides in a plane between the two new nuclei, and in this 

 plane a wall of cellulose is secreted. The foregoing is the 

 indirect or mitotic cell-division, and the nuclear changes 

 constitute karyokinesis. Some cells undergo direct or 

 amitotic division, the nuclei separating at once into two 

 parts without the intervention of the karyokinetic stages. 



17. Cell-division always results in an increase in the 

 number of cells, and is the usual process by which plants 

 are increased in size, and in the number of their cells. 

 Growth may be very rapid, even where the cells simply 

 divide successively into two. Thus a single cell may give 

 rise in its first division to two cells, next to four, then 

 eight, then sixteen, thirty-two, sixty-four, etc. etc. By 

 the twentieth division the cells would exceed a million in 

 number. 



18. The process of cell-formation by Union is exactly 

 opposite to that by Division. Two cells which were sepa- 

 rate unite their protoplasm into one mass, which then 

 forms .a cell-wall around itself. Thus instead of doubling 

 the number of cells at every step, there is here an actual 

 decrease, and every time the process occurs the result is 

 but half as many cells as before (Fig. 73, A, B, C). 



Practical Studies. — (a) Carefully scrape off (after moistening with 

 a drop of alcohol) a little of the white, mouldy growth on lilac-leaves, 

 known as Lilac Mildew ; mount it in water, adding a very little po- 

 tassic hydrate. Some of the threads will show the formation of new 



