12 BOTANY. 



cells (spores in this case) by fission. Other kinds of mildews, as for 

 example that on grass-leaves or that common on the leaves of cherry- 

 sprouts, furnish equally good examples. (See Fig. 97, p. 175.) 



(J) Strip off carefully a bit of the epidermis of a young Live-for- 

 ever leaf, and mount it in water. By careful examination some of 

 the cells may he observed with very thin partition -walls formed 

 across them. The new walls can be distinguished from the older 

 ones by their thinness. 



(c) Mount a very small drop of yeast in water and observe in the 

 yeast-plants that modification of fission which is called budding. 



Each yeast-plant is a minute oval 

 cell ; it first pushes out a little pro- 

 trusion which becomes larger and 

 larger, finally equalling the first. 

 In the mean time a partition forms be- 

 tween the two, which then separate 

 from one another. (Fig. 7, a and ft.) 

 FiQ. 7.— Yeast-plants repro- {d) Grow some yeast for a few days 

 ducing by Division : a and h by under a bell-iar on a moist slab of plas- 

 budding; c and d by internal •" '^ 



cell-division. Highly magni- ter, a cut potato or carrot, or even a 



^^^- bit of moist brown paper. Upon ex- 



amining such yeast it will be found that some of the cells con- 

 tain several little new cells, formed by internal cell-division. (Fig. 

 7, c and d.) 



(e) Make very thin cross-sections of young flower-buds so as to 

 cut through the stamens. If the specimen is of the proper age, cer- 

 tain cells may be seen to have divided internally into four parts, each 

 of which subsequently becomes a pollen grain having a thick cell- 

 wall of its own. 



(/) By carefully staining very thin sections of the preceding (e) 

 several of the successive stages of cell-division may sometimes be 

 seen by the aid of high powers of the microscope. They may be 

 seen also in the stamen-hairs of the Spiderwort, and the embryo-sac 

 of Fritillaria, hut for the successful study of karyokinesis the proto- 

 plasm must first be suddenly killed in chromic acid, absolute alco- 

 hol, or some other substance, and then very carefully sectioned and 

 stained. (See g, page 6.) 



(g) Good examples of cell-formation by Union may be studied in 

 any of the common Pond Scums (Spirogyra) to be found in every 

 pond in summer and autumn. 



19. Chromatophores. — Three varieties of chromatophores 

 occur in plants, as follows; 



