ACTION OP THE EFIDERMIS. 59 



collects upon their surface. If such impurities are constantly washed off, 

 plants wUl grow as well in cities as in country places. This was found 

 experimentally by M. Grarreau, who in the course of his inquiries into 

 the functions of the skin of plants, found that soap and water had great 

 value ; plants well washed acquiring a power of absorption much 

 beyond what they possessed ia their unwashed condition. Thus the 

 rate of absorption in the Tangiers Ferula was as 4 to after ablution ; 

 and in the yellow Grentian as 30 to 20. In like manner, the petals of 

 the Pseony took up five and six times as much after as before being 

 cleaned ; and the leaves of the Lilao, Lily of the VaUey, Ivy, and 

 Clematis about twice as much. It was found that soap and water had 

 a far greater cleansing effect than mere water ; thus, a Pig-leaf, which 

 had been lathered, absorbed 90 parts, while after a mere water-bath it 

 took up only half the quantity ; and a bramble, which soap and water 

 provided with 130 parts of water absorbed, could only consume 10 parts 

 when cleaned with water alone. It was thus shown that perfect 

 cleanliness is as indispensable to plants as to animals, and that dirty 

 gardening is necessarily bad gardening. Plants breathe by their 

 leaves ; and if their surface is clogged by dirt of whatever kind, their 

 breathing is impeded or prevented. Plants perspire by their leaves ; 

 and dirt prevents their perspiration. Plants feed by their leaves, and 

 dirt prevents their feeding. So that breathing, perspiration, and food, 

 are fatally interrupted by the accumulation of. foreign matters upon 

 leaves. Let any one, after reading this, cast an eye upon the state of 

 plants in sitting-rooms, or ill-kept greenhouses ; let them draw a white 

 handkerchief over the surface of such plants, or a piece of smooth white 

 leather, if they desire to know how far they are from being as clean as 

 their nature requires. Half the business of a good gardener consists 

 in sponging and washing the leaves of his plants. 



As the leaf is an extension of the rind of a stem, its 

 epidermis is also an extension of the skin of the same part; 

 and hence it is that in plants which produce no true leaves,' 

 such as the Stapelia, the office of the leaf is performed by the 

 rind and epidermis of the hark. 



The functions of respiration, perspiration, and digestion, 

 which are the particular offices of leaves, are essential to the 

 health of a plant ; its healthiness being iu proportion to the 

 degree in which these functions are duly performed. Conse- 

 quently, whatever tends to impede the free action of leaves, 

 tends also to diminish the healthiness of a plant. 



One of the translators of this work objects to the word digestion 

 employed in the preceding paragraph, upon the ground that the essen- 



