PHYSIOLOGY. 



273 



on the under surfaces of Spearmint, Elder (Sambucus rate 

 mosa,} Lilac, Clove Pink (Dianthus caryophyllus,) Mezerou 

 (Daphne mezercum) ; and on both sides of the Wild Spinacle, 

 African Geranium (Pelargonium), Everlasting Pea (Lathyrus 

 latifolius,) Fennel, and some others. 



Fig. 245. 



As an example of the hexagonal form 

 of these pores, we give Fig. 245, which 

 represents those on the under side of 

 the leaves of the Aloe, the Air-flower 

 (Epidendron,) Primrose, and others. 



In respect to size, these apertures difTer greatly in differ- 

 ent plants. The largest yet found are on the under side of 

 the leaves of the Oleander (Nefiurn Oleander.) It is a 

 simple oval puncture guarded by hairs, which cross the 

 opening in every direction. 



This subject has so excited the curiosity of vegetable 

 Physiologists that they have taken the pains to count the 

 number of pores contained within an inch square of surface 

 in the leaves of various plants, and from which the following 

 tabular statement has been drawn up. Some leaves, as we 

 have already seen, have pores on the upper, and none on the 

 under side, while others have them only on the undej; sidn 

 and others on both sides. 



