148 Dr Greville's Description of 



ART. II. — Description of two new Species of Marine AlgcB. By 

 Robert Kaye Greville, LL.D. F.R.S.E. F.L.S. &c. ; with 

 a Plate, 



In the formation of various genera, proposed in my work on 

 the AlgcB of the British Islands, I have ventured to deviate from 

 the rule laid down by ray excellent friend Agardh, and some 

 other algologists, — that the fructification shall constitute the 

 primary distinction. As plants are grouped together in order to 

 facilitate the labours of the botanist, it follows, that the greater 

 the resemblance between the individuals composing families and 

 genera, the more will such an object be fulfilled. Characters 

 ought therefore to be selected, which are not only constant, but, 

 if possible, conspicuous, and of easy application. In regard to 

 the organs of fructification, I agree entirely with Professor 

 Lindley, who observes, in his admirable work — the Introduction 

 to the Natural System of Botany — that they " are only entitled 

 to a superior degree of consideration, when found by experience 

 to be less liable to variation than those of vegetation. " Now 

 it is well known to the cryptogamic botanist, that he cannot 

 always draw his best characters from the organs of fructification ; 

 and that, even when he does so, situation is often taken into 

 account, as in the genera Hypnum and Bryum among mosses. 

 The form of the sorus is considered of importance among ferns ; 

 and in some cases, where the habit is very peculiar, that circum- 

 stance is considered as nearly sufficient of itself to establish 

 a genus. The lower we descend in the scale of vegetation, the 

 more variable do we find the organs of fructification to become, 

 and the characters we derive from them can hardly be considered, 

 in many cases at least, analogous with those taken from the same 

 organs in dicotyledonous and monocotyledonous plants. Besides, 

 any remarkable and at the same time permanent difference in the 

 vegetating medium, will naturally produce a new series of phe- 

 nomena, some of which may be of great importance. Under such 

 circumstances, vegetation may be found worthy of taking a 

 prominent part in the diagnosis of genera : and colour also, of 

 comparatively trifling value in other cases, may be sufficient, 

 among the marine algae, to distinguish, not only between families, 

 but between genera. 



Phyllophora, Ore v. — Alg. Brit. p. Ivi, 



P. ohtusa ; fronde subcartilaginea, palmata, segmentis apice 

 rotundatis, margine integerrimo, capsulis sphaericis in foliolis 

 stipitatis, disco frondis coacervatis. 



Hab. At the Cape of Good Hope. Bowie. 



Root, a hard disk. Stems, somewhat tufted, a few lines to an 

 inch in length, which soon expand into fronds, six to nine inches 

 long or more, divided in a palmate manner ; the segments nearly 



