ECTOCARPACE.E. 53 



at intervals, constitute a spongy, compound frond. The 

 fructification is perhaps of two kinds; the first, or spore, 

 being oval or spherical, furnished with a pellucid skin or 

 perispore and containing a dark coloured granular mass. 

 Such spores are sometimes sessile, sometimes stalked, and 

 either scattered over the branches or confined to particular 

 parts of the frond. The second description of fruit (called 

 propagulum by Agardh) is in Ectocarpus lanceolate or 

 linear, often shaped like a pod, or sometimes conical, trans- 

 versely striate, and containing an olive, granular substance; in 

 Sphacelaria it is mostly club-shaped, and contained in the 

 distended tips of the branches and ramuli. The plants 

 of this order are seldom gelatinous : some of the more deli- 

 cate kinds are very soft, and liable to be rapidly decomposed; 

 but the majority are membranous, and almost all of the first 

 sub-order are of a singularly rigid, almost horny substance. 

 The colour varies from dark brown to pale greenish ^olive, 

 and is subject to a little change in fresh water. 



This order is closely connected with the last, especially 

 through the genera Myrionema and Elachistea, the latter of 

 which is, by J. Agardh, placed here. The free filaments of 

 that genus do indeed associate well with the similar filaments 

 of the simple Ectocarpi, but the remaining part of the 

 organization has so much in common with Leathesia, an un- 

 doubted Chordariaceous plant, that I am unwilling to place 

 it in a different order. 



Continental authors, in general, regard our two sub- 

 orders as distinct ordinal assemblages, and in the system of 

 Endlicher they are widely separated from each other. To 

 me the connection between them appears close ; the differ- 

 ence chiefly technical, one being a simpler form of the 

 other, and I am unwilling to sanction what seems an 

 unnecessary division of orders. Such plants as Ectocarpus 

 Mertensii are nearly intermediate between the two groups. 



The Ectocarpacea? are the least compound, the lowest in 

 organization, of the olive-coloured Alga3, yet among them 

 we find, as not rarely happens in similar cases, some of the 

 most elegant and delicately beautiful structures of the group. 

 None are of large size, and many require the aid of the mi- 

 croscope to develope their full beauty. The genera, and 

 several of the more common species, are very widely dis- 

 persed, nor are there any generic forms known which are not 

 represented in our flora. 



