52 Importance of Cleanliness to Plants. 



those openings. The fact that the epidermis of leaves will 

 not permit the passage of water in their natural state, but 

 wUl do so when the greasy matter which coats their surfaces 

 is artificially removed, may be proved by immersing a faded 

 leaf for some hours in water, keeping the whole of the leaf- 

 stalk out of the fluid, it will absorb little or no water ; but 

 if it has been previously carefully washed with soap in dis- 

 tilled water, it will then be able to absorb a very notable 

 quantity of the water in which it is subsequently immersed. 

 This absorption is found to be quite as great in those leaves 

 which are furnished with very few stomata, as it is in those 

 which have many, provided the washing be carefully con- 

 ducted, and all pressure avoided, v.iiich would cause the 

 forcible introduction of water through the stomata. 



The chief conclusions to which M. Garreau arrives, as the 

 results of these and a number of similar experiments, are as 

 follows : — Firstly, that the cuticle of plants possesses the 

 power of allowing endosmosis to take place whilst the parts 

 are young, but that it loses it as they grow old. Secondly, 

 that this power is in proportion to the quantity of oleaginous 

 matter which exists in the cuticle, being greatest in those 

 membranes which contain least fatty matter, or in which it 

 has been artificially removed by washing. Thirdly, that the 

 cuticle which covers the upper surface of the nerves, and 

 particularly that which clothes the axillary part of the leaf- 

 stalk, is that which permits the most abundant endosmosis. 

 Fourthly, that the epidermis sometimes interferes with this 

 power of the cuticle, because plants which have no epidermis 

 permit endosmosis to a remarkable extent ; and young bark 

 which has this organ, permits much less endosmosis than 

 that which is without it : and lastly, that if simple washing 

 with distilled water is able to increase the absorbent power 

 of leaves, it is plain that rain water must produce the same 

 effect. 



These results are certainly highly interesting, and unques- 

 tionably point to a new and hitherto unsuspected offi.ce of 

 rain^ they show the importance of keeping the surface of 

 plants clean, and lead to numerous useful hints to the prac- 



