188 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



and Cruoria, J. Ag. Peyssonnelia grows on shells and other 

 marine bodies, and extends from the Mediterranean to Ireland, 

 and the opposite Atlantic shore of North America. The 

 analogy between this genus and Ralfsia, is very striking. A 

 number of other plants of similar habits, adhering under 

 the form of an almost inseparable crust, with one or two which 

 grow upon such Alga as Phyllophora rubens, but of doubtful 

 affinities, in consequence of our comparative ignorance of their 

 fructification, have been placed here by Agardh, jun. Several 

 of these, as Petrocelis cruenta, Hildenhrantia Orouani, H. 

 rivularis, Contarinia PeyssonTieliwformis, and probably 

 several others, occur on our coasts ; for almost all belong to the 

 temperate seas of the northern hemisphere. One alone has at 

 present occurred in Australia. Peyssonnelice also occur at 

 Port Natal, under two forms. As far as these plants are known 

 there is very little to separate them from the squamasform 

 corallines, except the absence of calcareous matter. The 

 fruit, though contained in conceptacles, as in Hildenhrantia, is 

 really in the form of tetraspores, as in corallines. If this be 

 not conceptacular, that form of fruit is at present wholly 

 unknown. Petrocelis cruenta* is a curious microscopic object. 

 Dr. Harvey found certain swellings in the threads, con- 

 iined to a single joint, the nature of which he could not deter- 

 mine, but in a specimen in my herbarium, from Mr. Ralfs, 

 I find these converted into tetraspores (Fig. 45, d) as distinctly 

 as in any other Rhodosperm. The same specimen, moreover, 

 shows beneath distinct lines of growth. I find the length of 

 the joints extremely variable. In Scotch specimens the fila- 

 ments are disposed in little fascicles, and there is something of 

 the same structure, but not so evident, in other specimens. In 



* Tliis is Cruoria pettita of Fries and Harvey. I believe the plants 

 of Areschoug, Lyngbye, Flora Danica, and Harvey to be identical. I 

 have in vain sought for fruit in the plant of Desmazifires, which is that 

 in which Agardh has seen fruit different from that here figured, and 

 on which he hag founded his genus Cruoria. As regards the mere 

 threads, it does not differ from specimens from Carmichael and Balfe. 

 In all, they are slightly branched above. J. Agardh has no evidence to 

 show that his Cruoria pelUta belongs to a different genus from his 

 Petrocelis cruenta. 



