OF THE ELEMENTARY STRUCTURES. 729 



while in the latter state, the exhalation is more or less prevented. 

 In all the above cases of adaptation of the epidermis and 

 stomata to the conditions under which plants are placed, it is 

 impossible not to be struck with the wonderful evidences of 

 Design exhibited. 



It is also through the cells of the epidermis, and more espe- 

 ciaUj through the stomata, that certain gaseous matters are 

 absorbed from, and exhaled into, the atmosphere, in the processes 

 of Respiration and Assimilation. (See these processes.) 



Hairs and their modifications, appear to be designed, to protect 

 the epidermis and parts beneath from injury from cold and other 

 external influences, hence, we find young buds, &c., frequently 

 coated with hairs. Hairs also appear in certain instances, at 

 least to some extent, to absorb fluid matters from the atmo- 

 sphere, &c. ; whilst in other cases, they serve to assist the epir 

 dermis in restraining exhalation, and we find accordingly, that 

 plants which are densely coated with them, are well adapted to 

 grow in dry arid situations, and to withstand without injury a 

 season of drought. 



Glands are those organs which contain some of the peculiar se- 

 cretions of the plant. These secretions are either permanently 

 stored up in them, or excreted. 



It is still a disputed question whether the epidermal tissue 

 and its appendages have the power of absorbing hquids, such 

 as water. Some authors, as linger, not only deny the pos- 

 session of such a power, but also that of taking up watery 

 vapour. We think, however, that there can be no doubt upon 

 the latter point, for otherwise, how is it possible to account for 

 the immediate recovery of drooping plants in a greenhouse, 

 when water is sprinkled upon the floors, &c., or the revival upon 

 a large extent in nature, of vegetation, when a mist follows a 

 long succession of dry weather, — except by believing that watery 

 vapour is taken up by the epidermal tissue and its appendages ? 

 Whether water itself is absorbed by the epidermal tissue and 

 its appendages is very doubtful. Various experimenters have 

 endeavoured to show that they have this power. The researches 

 of Garreau led him to the following conclusions : — 1. That the 

 cuticle possessed an evident endosmotic property, the intensity 

 of which was in proportion to the age of the tissues which it 

 invested ; thus it was greatest when they were young, and 

 gradually diminished as they approached maturity, and was alto- 

 gether lost when they became old. 2. The absorption of the 

 cuticle was greater in proportion to the absence of waxy or fatty 

 matters. 3. The cuticle covering the upper surface of the ribs, 

 and especially of that of the petiole where it joins the stem, is 

 that part of the leaf surface which presents the most marked 

 power of absorption. 4. In certain instances in which the cu- 

 ticle is absorbent, the epidermis presents impediments to ab- 



