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 

 OF IRIS (Osterhout). 



Fu;. 115. STOMATE OF IVY, 

 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. 



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

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



Peony .......... 13*790 None 



Holly .......... 63,600 None 



Lilac .......... 160,000 None 



Mistletoe ......... 200 200 



Tradescantia ........ 2.000 2,000 



Garden Flag (iris) ...... Uj572 n>572 



The arrangement of stomates on the leaf differs wtih 

 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, 



FIG." lie! -STOMATES n dther side the P enin g- One 

 OF GERANIUM LEAF. method of opening is as follows : The 



