Bibliographical Notices. 113 



law, propounded by our author himself, which may be regarded as a 

 sort of corollary to the former. 



In the lowest cellular plants every part of the surface appears 

 equally concerned in the function of absorption. This is most evi- 

 dent in those simple protophytes usually classed among the Algce, 

 which consist of an aggregation of insulated vesicles, each of which 

 may almost be regarded as a distinct individual. Thus the surface of 

 one of the cells of the Protococcus nivalis may be regarded as all root. 

 In the higher genera of this group the separate vesicles no longer 

 maintain their individuality, but form part of one definite structure. 

 Still the whole surface appears to be endowed with the power of ab- 

 sorption in nearly an equal degree ; and though the semblance of a 

 stem and roots occasionally presents itself, these appear to have no 

 other function than to give attachment to the frondose expansion. 

 There is no transmission of fluid from one part to another, each cell 

 deriving from the surrounding medium, or from the surcharged cells 

 in its immediate neighbourhood, the fluid essential to its existence. 

 It is in the Lichens that we find the first specialization of the absorb- 

 ent function, by the restriction of it to the side least exposed to the 

 sun and air, whilst the reproductive function, which in the Algce was 

 common to nearly the whole frond, is here confined to the other sur- 

 face. In some lichens we find radical filaments developed from the 

 absorbent surface, the first indication of special organs for the pur- 

 pose. In the Fungi the separation between the nutrient and repro- 

 ductive organs is generally still more complete, and in the highest 

 groups of this order a stem with very definite roots is developed. 

 These are yet more complete in the mosses, but still nutrition may 

 be performed by the general surface independently of them. And 

 even where these filamentous processes of the Cryptogamia bear the 

 greatest resemblance to roots, there is reason to believe that they ab- 

 sorb by their whole surface, and not by their points alone. In the 

 vascular plants we find the function of absorption attaining its high- 

 est degree of specialization, being as it were concentrated in the 

 growing points of the roots, which are known as the spongioles, and 

 the function is more actively performed by them in proportion to the 

 small amount of surface they expose. 



Still, however, it is found that the general surface, even of a 

 vascular plant, is concerned in this function, and that in many in- 

 stances it is even capable of entirely performing it when the roots 

 are from any cause unable to act. This is a very beautiful example 

 of the second law to which we have alluded, and which we shall 

 state in the author's words. *' In cases where the different functions 



