A PEEP AT THE INSIDE, 73 



(Fig. 65.) These openings are the breath- 

 ing pores or stomata, and they are situ- 

 ated directly over air spaces. The crescent- 

 shaped cells are called the guard cells of the 

 stomata, and they have the power of regu- 

 lating the size of the opening into the leaf, 

 often completely closing it. The grains in 

 the cells of Fig. 64 represent the pigment 

 which gives the green color to the leaf ; these 

 are the chlorophyll grains, "leaf -green" 

 grains. Although they usually occupy but 

 a portion of the cell, they are still so close 

 together as not to be recognized by the eye, 

 and they therefore present a continuous ap- 

 pearance of gTeen. The epidermis, both 

 above and below, is mostly destitute of chlo- 

 rophyll, and transparent. The cell contents 

 are as variable as the cells themselves. All 

 growing parts contain a whitish granular 

 liquid known as protoplasm. This proto- 

 plasm is the life-giving element of plants, 

 from which are formed new cells, and starch 

 and other products which the plant stores 

 up for future use. All seeds and tubers and 

 bulbs store away starch to feed the plantlet 

 while it is germinating and establishing it- 

 self in the soil. 



We have before remarked that all plants 



