102 Mr Carpenter on Unity of Function 



eel to seem to prove. Here, then, is the lowest degree of spe- 

 ciaHzation of the function of absorption in the animal kingdom ; 

 and perhaps we may regard the condition of the absorbent sur- 

 face in the lichens as somewhat analogous to it, since in these 

 it is generally only one surface that absoi'bs freely, namely, the 

 one least exposed to the sun and air. The first appearance, 

 however, of any extension of the surface for this purpose (such 

 as we find in the radical fibres of some fungi, but more particu- 

 larly in the mosses), takes place by an external prolongation ; 

 and we may therefore consider Fig. 2. as illustrat- 

 ing, in contrast with Fig. 1, what may be regarded 

 as the type of the absorbent system in plants. The 

 final cause of this difference in the direction of de- 

 velopment will subsequently come to be considered. 



Now, it will be remarked, that as soon as a particular part 

 of the surface is modified for absorption, the tissues in general 

 derive their nutriment indirectly through the medium of a 

 circulating system, however imperfect. The organs of circula- 

 tion are therefore to be regarded, not as essential to our idea 

 of a living being, but as superadded in those cases where the 

 transmission of fluid from one part to another has become ne- 

 cessary. Cuvier endeavoured to shew that the development of 

 the organs of circulation in animals proceeds pari passu with 

 that of a distinct respiratory system ; I think it is evident, how- 

 ever, that we arc to look for the fundamental cause of both 

 in the specialization of the absorbent surface, through which 

 the aliment is introduced which is to undergo subsequent 

 change. We find in the mosses and fungi more or less se- 

 paration of the nutritive apparatus from the rest of the plant, 

 by a distinct axis of growth or stem ; and in this we find the 

 cells elongated in such a manner as to approach the form of 

 vessels. In the Algae, on the other hand, where there is no 

 necessity for any transmission of fluid, the cells approach more 

 to the normal spherical form ; and if one part of the frond be 

 taken out of the water, it will wither, although tlie rest be ac- 

 tively vegetating. In ascending through the scale of cellular 

 plants, we find the absorbent system becoming more and more 

 specialized, and the vascular communication more complete, 

 until we find in the Phanerogamia the extremity only of the 



