117 



they cease first at the apex, which becomes hyaline 

 and elongate, and eventually continue only in 

 places here and there. The filaments, simple or 

 branched, are for the most part of one single cell- 

 row and rarely divided by longitudinal walls. Some- 

 times the cells of the erect filaments produce rhizoids 

 which descending form a loose weft about the shoot. 

 Where a basal horizontal layer occurs (e.g., Ascocydus 

 and Phycocelis) it grows by peripheral cell-divisions 

 and bears on its upper surface sporangia, hairs and 

 paraphyses. 



The Reproductive, Organs. The plurilocular spor- 

 angia, which may be of one or more rows of loculi, are 

 formed either by the differentiation of the upper por- 

 tion of a branch or an intercalary part of it ; or they 

 are definite outgrowths of cells of the erect filaments 

 or primary basal layer. In Sorocarpus they occur in 

 dense clusters ; but in the other genera they are free 

 like the branches and mostly elongate, cylindrical, or 

 oval in shape. They are commonly of several rows 

 of loculi, but sometimes of a single row, wholly or in 

 part. The gametes escape from all the loculi usually 

 by an apical or lateral opening, and their conjuga- 

 tion is of a peculiar character. In Ectocarpus silicu- 

 losus, in which it has been carefully observed, the 9 

 gamete first comes to rest and is then surrounded by 

 numerous ^ gametes, one of which succeeds in con- 

 jugating with the $ gamete. That the $ gamete 

 should first come to rest before becoming susceptible 

 of conjugation recalls the case of CiMcria, and also 

 in part that of Myriotrichia. The occurrence of 

 bodies which can only be termed antheridia in 



