" throughout the bay, but is confined to the space of a few rocks, 

 on which it forms, as it were, a colony, or is gregarious.' ' It 

 appears by no means indifferent to what plant it attaches its 

 fronds, being very generally found growing on Ptilota sericea, 

 though frequently also on Cladophora rupestris. I am not aware 

 that it ever infests any other Algse. 



The nearest affinity is with E. brachiatus (PL IV.), from 

 which it is most readily known by the difference in the fruit, the 

 spores being in that species lodged in swellings or enlargements 

 of the smaller branches in the axils of the opposite ramuli j and 

 in this being formed by a metamorphosis of the ramuli them- 

 selves. My friend, Professor Kiitzing, strongly urges that this 

 difference indicates, not a different species, but a different con- 

 dition of the same species : in like manner as the two modes of 

 fructification found in the Floridece are not to be regarded as 

 specific characters. There is something, certainly, still to be 

 cleared up respecting the fructification of the Ectocarpi, to recon- 

 cile the varying appearances which the organs of reproduction 

 assume in different species. Nevertheless I am disposed to 

 retain the present species distinct from E. brachiatus, at least, 

 until their identity be proved ; because, independently of fructi- 

 fication, there is a difference in aspect, more readily seen than 

 described in words, and because they are found as parasites upon 

 different Algae. Both species have been collected and observed 

 by very accurate botanists, who do not find them intermixed, 

 and are firmly persuaded that they are essentially different. 



Dr. J. D. Hooker brought from Cape Horn an Ectocarpus (E. 

 geminatus, Hook. fil. et Harv.) closely resembling our E. spkcsro- 

 p/wrus, and also forming spores by an alteration of the ramuli ; 

 but its spores are of a conical, not spherical, form. It would be 

 very interesting should future observations detect this analogous 

 species on the shores of the Shetland Islands. 



Fig. 1. Ectocarpus spileropiiorus; a tuft: — of the natural size, growing on 

 a fragment of Ptilota sericea. 2. Portion of a branch. 3. Ramuli, with 

 spores : — both niaguijicd. 



