ABSORPTION. 



ABSORPTION. 



is they that effect the removal of parts which 

 disappear without the action of externa 

 agents. The lymphatics ultimately empty 

 their contents into the same vessel as the lac- 

 teals ; and they follow, in their distribution 

 through the body, the same course as the 

 veins. In the horse they are liable to a dis- 

 ease termed farcy ; and in all animals they a^e 

 frequently inflamed in the neighbourhood of a 

 sore. The absorbents, both lacteals and lym* 

 phatics, are very delicate in their sides, nearly 

 transparent, have numerous valves which 

 compel their contents to flow only in one di- 

 rection ; and their larger trunks have numerous 

 glandular bodies on them. The use of these 

 glands is not well known ; but, from one or 

 two circumstances, it would appear that they 

 have to produce some change on the fluid 

 which passes through them before it is fit to 

 mingle with the blood. 



ABSORPTION. An important process in 

 vegetable physiology. As plants are not fur- 

 nished with any individual organ similar to 

 the mouth of animals, how, it may be asked, 

 do they effect the introduction of food into 

 their" bodies ; Is it by the general surface of 

 their stem, leaves, or roots, or by any peculiar 

 part of these 1 By whatever part it may enter, 

 it must, at any rate, pass through the covering 

 of the outer bark (epidermis'}, which the earlier 

 physiologists thought it could not do, but by 

 means of pores more or less visible. Yet 

 some of them describe the outer bark as being 

 so close and compact a texture, that the eye, 

 aided even by the best microscopes, was un- 

 able to discover in it the slightest vestige 

 either of pores or of apertures. But Hedwig 

 and De Candolle detected superficial pores in 

 the leaves, at least, of many plants ; and so 

 will any one else, who will be at the trouble 

 of repeating their observations with lenses of 

 similar powers. 



The next difficulty was with regard to the 

 outer bark (epidermis') of the flower, fruit, and 

 root. No pores had been detected in the 

 flower and fruit, though it was evident that 

 they were refreshed and invigorated by the ac- 

 cess of moisture and of atmospheric air ; and 

 no pores had been detected in the root, though 

 it was evident that the whole of the nourish- 

 ment which the plant derives from the soil 

 must of necessity pass through the root. It 

 was also evident that no aliment could be 

 taken up by the plant, except in the state of a 

 liquid, or of a gass that is, by absorption or 

 by inhalation, as the chyle is taken upinto^the 

 animal lacteals, or the air into the cells of 'the 

 lungs. The greediness with which plants ab- 

 sorb water was perceived and acknowledged 

 even in the earliest times, and even by men 

 who were not botanists. Anacreon, in one of 

 his little trifles in honour of drinking, makes 

 the very trees of the forest drink : 



'H yfj (jc\niva irfpci, 



TLivev Si SivSpe' avrfiv. Ode xix. 



" The black earth drinks, and the trees drink it ;" 



that is the moisture which it contains. 



By merely immersing in water a plant of 

 almost any species of moss that has been 

 some time gathered, or long exposed to 

 2 



drought, so as to have had its leaves shrivel- 

 led up, the moisture will immediately begin to 

 penetrate the plant, which will thereby resume 

 its original verdure; an experiment which 

 proves the fact of the entrance of moisture 

 into the plant through the outer bark (epider* 

 mis'). 



It might be doubted whether any of the 

 moisture thus imbibed had passed through the 

 root. But if the bulb of a hyacinth is placed on 

 the mouth of a glass bottle filled with water, 

 so as that the smaller roots (rud/clr*) only 

 shall be immersed, the water is imperceptibly 

 exhausted, and the plant grows. The mois- 

 ture must, consequently, have passed through 

 the root. Plants seem, indeed, to be peculiarly 

 well adapted for the absorption of fluids by the 

 roots, from the infinite number of little absor- 

 bent fibulous sponges (spangiolss\ in \vhich 

 the fine fibres of the root terminate. It is 

 owing to this important property that the 

 scientific gardener, in the transplanting of his 

 young trees, or the scientific and ornamental 

 planter, irr the transplanting of his trees of 

 full growth, is so extremely careful to pre- 

 serve entire even the minutest fibres and ex- 

 tremities of the root. Sir Henry Steuart's 

 Planter's Guide has taught him the great im- 

 portance of these little organs. 



Hales instituted a variety of experiments to 

 show the absorbing power of roots, and the 

 force with which it acted; as did also Duha- 

 mel and Marriotte, to show the absorbent 

 power of leaves. But the most complete set 

 of experiments upon the absorbent power of 

 leaves is that of M. Bonnet, of Geneva, whose 

 main object was to ascertain whether the ap- 

 sorbing power of both surfaces of a leaf was 

 alike. With this view he placed a number of 

 leaves over water, so as that they only floated 

 on it, but where not immersed ; some with the 

 upper surface, and others with the under sur- 

 face, applied to the water. If the leaf retained 

 its verdure the longer with the upper surface 

 on the water, the absorbing power of the upper 

 surface was to be regarded as the greater ; but 

 if it retained its verdure the longer with the 

 under surface on the water, then the absorbing 

 power of the under surface was to be regarded 

 as the greater. Some leaves were found to re- 

 ;ain their verdure the longer when moistened 

 by the upper surface, and some when moist- 

 med by the under surface; and some were 

 ndifferent to the mode in which they were ap- 

 alied to the water. But the inference cleduci- 

 :>le from the whole, and deduced accordingly 

 y Bonnet, was that the leaves of herbs absorb 

 moisture chiefly by the upper surface, and the 

 eaves of trees chiefly by the under surface. 

 What is the cause of 'this singular difference 

 between the absorbing surfaces of the leaf of 

 the herb, and of the tree 1 The physical cauas 

 might be the existence of a greater, or of a 

 smaller number of pores, found in the leaves 

 of the herb and tree respectively. The chemi- 

 cal cause would be the peculiar degree of affi- 

 nity existing between the absorbing organs and 

 the fluid absorbed. Duhamel seems to have 

 been content to look to the physical cause, 

 merely regarding the lower surface of the leaf 

 of the tree as being endowed with the greater 



