4 PLANT LIFE. 



7. Centrospheres. — The centrospheres are intimately re- 

 lated to the nucleus. They are two very minute spherical 

 bodies lying in contact with it (figs, i, 2). When the 

 nucleus is about to divide one centrosphere goes to each 

 pole (fig. 2, B), and the separation of the nuclear material 

 occurs near the nuclear equator. Just as this occurs the 

 centrospheres divide, forming a pair at each pole. Two 

 accompany each daughter-nucleus. Their purpose is not 

 yet fully understood. 



•••28 



Fig. 



Fig. 



Fig. 



t, showing its 



wall, and some 

 il-drop. Mag- 



Fig. 3. — A cell from the interior of the leaf of the 

 inclusions of the cytoplasm, z, the nucleus; c, chloropla 

 nified about ioo diam —After Zimmermann. 



Fig. 4. — A, chloroplasts from the skin of the petiole of ivy; B, from the inner leaf- 

 cells of morning-glory; C, from the same cells of Achyranthes. The shaded parts 

 are protoplasm in which are embedded starch-granules, j, and proteid crystalloids, 

 k. Magnified about iooo diam. — After Zimmermann. 



Fig. 5.- — Leucoplasts from a young shoot of Canna. The shaded part is protoplasm, 

 in which are embedded starch-grains, s, and proteid crystalloids, k. Magnified 

 about 1000 diam. — After Schimper. 



8. Plastids. — In most cells there are also other protoplas- 

 mic structures, the plastids. In young cells these are small, 

 rounded, colorless bodies. As the cell grows older they in- 

 crease in size and number. At maturity, in cells which lie 

 near the surface of green plants, they are commonly roundish 

 or biscuit-shaped, of spongy texture, and colored yellowish- 



