186 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



favelte of that genus, with their indefinite spores, and the 

 monihform spore-threads of this. (Fig. 45, c.) The genus is 

 not confined to the southern seas, or Europe, but occurs also 

 both at Key West, in North America, and at Vera Cruz, where 

 it was found by Liebmann. Naccaria also occurs on our 

 coasts, and differs remarkably from Wrangelia in its inarticu- 

 late frond. This, however, is merely a question of degree. In the 

 structure of the fruit both agree perfectly, as far as the spore- 

 threads and spores are concerned ; but in one they invest the 

 short swollen fructifying branchlets, in the other they are 

 formed at the truncated tips. In Wrangelia, that is, they are 

 more condensed than in Naccavia. 



6. Helminthocladi^, J. Ag. 



Frond more or less gelatinous, essentially filamentous, though 

 closely compacted. Nucleus immersed without any concep- 

 tacle, formed of radiating sporiferous threads. 



162. In each of the three great divisions of Algaj, there is a 

 group separated from the rest, by peculiar habit and simila- 

 rity of structure. A central thread or axis gives off, in its 

 course, a number of short, horizontal, close-packed branches ; 

 the whole constituting a flaccid, gelatinous, flexible frond, 

 which varies in colour with the division to which it belongs. 

 But, besides these three groups, there are genera with similar 

 habits, as Budresnaia, Crouania, and Gloeosiphonia, which 

 form representatives in Ceramiaceoi and Gryptonemiaceo}. 

 In the present instance the cylindrical frond is red. The 

 nucleus has no surrounding walls, but is immersed amongst 

 the constituent filaments and is composed of branched spore- 

 threads breaking up into spores. In the genus 8cinaia, how- 

 ever, both Dr. Montague and Harvey have seen, with greater 

 or less distinctness, a delicate membranous envelope. Tetra- 

 spores at present have been discovered in Nemalion only. 



163. As regards geogxaphical distribution, Liagora and 

 Scinaia are lovers of warm seas, and the former is common 

 everywhere in such situations, one species beiug found by 

 Messrs. Orouan at Brest, while the latter ascends as high as 

 the southern coasts of England, under the form of the old Ulva 

 furcellata. The other genera are either European or American, 



