88 



PLANT BIOLOGY 



sunlight. Fig. 114 shows the structure. There are two 

 guard-cells at the mouth of each stomate, which may in 

 most cases open or close the passage as the conditions 

 of the atmosphere may require. The guard-cells contain 



Fig. 114. — Diagram of Stomate Fig. 115. — Stomate of Iw, 



OF Ikis (Osterhout). showing compound guard-cells. 



chlorophyll. In Fig. 115 is shown a case in which there 

 are compound guard-cells, that of ivy. On the margins 

 of certain leaves, as of fuchsia, impatiens, cabbage, are 

 openings known as water-pores. 



Stoma tes are very numerous, as will be seen from the num- 

 bers showing the pores to each square inch of leaf surface : 



Lower surface Upper surface 



Peony J 379° None 



Holly 63,600 None 



Lilac 160,000 None 



Mistletoe 200 200 



Tradescantia 2.000 2,000 



Garden Flag (iris) 11.572 n,57 2 



The arrangement of stomates on the leaf differs with 



each kind of plant. Fig. 116 shows stomates and also the 



outlines of contiguous epidermal cells. 



The function or work of the stomates 



is to regulate the passage of gases into 



and out of the plant. The directly 



active organs or parts are guard-cells, 



on either side the opening. One 

 Fig. r 16. — Stomates t 



of Geranium Leaf. method of opening is as follows: The 



