590 MR JOHN RATTRAY ON ECTOCARPUS. 



tesselatus chiefly occur on Laminaria digitata and L. saccharina. On the other 

 hand, the host plants of E. littoralis and E. siliculosus are very numerous, the 

 latter, up to the present time, having been found on Cladophora rupestris, 

 Corallina officinalis, Chorda lomentaria, Chordaria fiagelliformis, Ceramium 

 Deslongcliampsii, Asperococcus echinatus, Halidrys siliquosa, Polysiphonia elon- 

 gata, P. urceolata, Myriotrichia clavarformis, and Rhodymenia palmata, in the 

 Firth of Forth.* Next to E. siliculosus and E. littoralis, E. sphairophorus is 

 that which is least restricted in its range of host plants, being chiefly found 

 associated with Rhodosperms (e.g., Callithamnia and Ptilotae). From this 

 peculiar habit the entire genus might be conveniently divided into two groups 

 — a smaller containing the non-epiphytic species, and a larger including all those 

 found growing on other algae. 



Ectocarpus siliculosus (Lyngb.), upon which my present observations are 

 founded, is an annual plant occurring chiefly from May to September, or, 

 according to HARVEY,t from "spring to autumn." As already indicated, this 

 species is found between the highest and lowest limits of the tide, and even 

 extends to depths varying from three to four fathoms. 



In general habit E. siliculosus is most closely allied to E. littoralis, but may 

 be distinguished from the latter by its more slender and somewhat softer 

 growth, and by the fact that its ramuli, which may be either alternate or subse- 

 cund, are never opposite — an arrangement which may occur in young branches 

 of E. littoralis. The multilocular sporangia, moreover, of the two species may 

 be readily distinguished, those of E. littoralis being placed in the middle of the 

 ramuli, while those of E. siliculosus are lanceolate aud terminal. 



In addition to the ordinary multilocular sporangia ( = Trichosporangia, Nob.) 

 upon whose true reproductive significance all observers are agreed, various 

 species of Ectocarpus have from time to time been found to possess so-called 

 " unilocular sporangia" ( = Oosporangia, Nob.) with regard to which there has 

 not been the same consensus of opinion among algologists. 



Thuret, \ when discussing the fructification of the Phaaosporeae, says : — " La 

 seule fructification que Ton signale dans ces plantes consiste en sporanges 

 ovoides (Oosporangia, Nob.), qui out d'ailleurs ete toujours decrits commc des 

 spores simples, quoique en realite" ils soient remplis de nombreux zoospores. 

 Get organe est le plus visible, et e'est ce qui explique pourquoi il a surtout 

 attire Fattention des observateurs. L'autre forme de sporanges consiste en 

 filaments cloisonnes. 



" (Trichosporangia, Nob.), fort dtroits et generalement assez courts, composes 

 dune series de petites cellules, dans chacune desquelles est renferne un zoospore. 



* Traill, Monograph of tin- Alga' of the Firth of Forth, 1885. 

 t Harvey, Phycologiu Britannica. 

 % Thuret, loc. cit., pp. 235-236. 



