212 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



197. Some authors separate Ectocarpi from the more com- 

 pound species ; but we have before seen amongst Ehodosperms, 

 that even in the same genus great differences exist in this 

 respect, and, taking all circumstances into consideration, I 

 think that Dr. Harvey is quite right in keeping plants together 

 so clearly associated by nature. 



2. Chordaei^, Harv. 



Frond compound, gelatinous, consisting of vertical and hori- 

 zontal threads, variously interlaced. Cysts contained in tlie 

 substance of the frond, attached to the horizontal threads, 

 giving rise to zoospores. 



198. The preceding group was remarkable for containing 

 both highly rigid and extremely flaccid species, but in both 

 cases devoid of gelatine, or, if not absolutely so, containing so 

 little as to present no salient character. The contrary is 

 eminently the case with most of the tenants of this division, 

 though connected with Ectocarpeoe, by species in which the 

 character is of no prominence. In some species the threads 

 are distinct above, though rising from a common cellular para- 

 sitic base, while in others they are felted into a more or less 

 compact mass, varying from an adnate stratum to globose 

 tuberous bodies, and thence to a branched or simple sHmy 

 cord, often many feet in length. 'The fruit, in most cases, is 

 twofold, consisting either of oblong cysts, or elongated and 

 often septate pods, both of which produce zoospores ; but 

 sometimes in the one, sometimes in the other, alone they have 

 been seen to germinate ; sometimes both are equally fertile. 

 The species, for the most part, are inhabitants of northern 

 climates, and more abundant in colder waters, though not con- 

 fined to them, and two of our commonest species, Leathesia 

 tuberiformis and Chordaria flagelliformis are equally com- 

 mon ia the southern hemisphere. The most curious group, 

 perhaps, is that of Elachistea, the species of which are para- 

 sitic on various Algse, and in some cases, as in Himanthalia 

 lorea and Elachistea scutulata, the connection between the 

 tissue of the matrix and the base of the parasite is so con- 

 tinuous as to have induced a belief that the species are merely 

 fibnormal developments of cellular tissue. Such notions might. 



