THE OEGANS AND PARTS OF PLANTS. 7 



roots, with numerous minute openings, called pores, which 

 are often smaller than pin-holes, and by which liquid food 

 in the soil, or that which is floating in the air, is freely 

 received. Until very recently, it was believed that the 

 nutriment of plants was obtained almost solely through 

 the roots. But it has now been proved that they can exist 

 loholly on atmospheric supplies, and that they draw very 

 largely from this resource at all times. The ^^ores there- 

 fore, are no doubt the means through which such nourish- 

 ment is appropriated. But they are also the agents by 

 w^hich evaporation is carried on, and probably £iir admitted. 

 Those on the leaf undoubtedly lead to small air-cells, and 

 they are j)Ossibly similar to the nostrils of animals, or the 

 pores in the human body, or rather to the breathing pores 

 in the sides of insects. The subjoined figures will convey 

 a good idea of the shape and nature of pores, as existing on 

 the leaves of plants ; and their resemblance to such as are 

 found in the sides of insects. 



Pores greatly magnified : a, a, pores of plants open ; 6, h, the 

 same shut ; c, breathing pore or spiracle in the side of a caterpillar 

 open ; the same shut. 



These figures represent the pores to have raised lips, 

 varying in form, which appear to shut when they are 

 wetted, and also in the dark, but open in dry air, and when 

 exposed to sunlight. Through these pores the plant gives 

 off two-thirds of its superfluous water, in a similar manner 

 to that in which animals do the same by the breath and by 

 perspiration. They perform, in fact, much the same offices 

 as the pores of the human body, which are easily proved 



