164 LEAVES 



which air is taken into the leaf and air and moisture are 

 given out. 



Compare the upper and under surfaces of the same leaf. 

 How do they compare in number of stomata ? Do your 

 observations in this respect agree with the results of experi- 

 ments on transpiration ? 



Note. The epidermis of iris, lily, onion, houseleek, and fern 

 are easily removed. 



147. CELLS (optional) 



Object. To demonstrate the cellular structure of 

 leaves. 



Method. Mount bits of skin of leaves or thin slices of 

 pith in water or glycerin and study the individual cells. 

 Make out the following points of cell structure : 

 (a) The cell wall. 

 (6) The cell contents (protoplasm). 



(c) The chloroplasts , or grains of yellowish green material 

 which are found in some of the cells. 



(d) The nucleus, a sort of kernel or denser mass usually 

 near the center of a living cell. 



If the nucleus is not clearly seen, place the section in 

 methyl green for a few minutes, and it will usually become 

 stained. 



Make drawings of as many different forms of cell as you 

 are able to find. 



Onion and lily epidermis have cells which are very unlike 

 those of fern. Pith cells are very unlike guard cells in shape. 



Root hairs are epidermal cells of the root which are pro- 

 longed outward, increasing the absorbing surface of the 

 root (Ex. 91). Cells of endosperms (Ex. 40) contain 

 starch. 



