Il8 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Acrochaetium affine sp. nov. 



Epiphytic, 1.0-3.5 mm. high, from a large persistent basal cell 

 (spore), this subglobose or ellipsoid, mostly 14-26^1 in diameter, 

 finally becoming subpyriform and 20-33 M high through the de- 

 velopment of a subcylindric obtuse or truncate foot penetrating 

 the host for about 10-24 ju, the basal cell remaining simple or 

 occasionally developing one or more smaller accessory cells, or 

 sometimes sending out short creeping, often more or less immersed, 

 filaments 2-5 cells long, these very rarely forming a small imperfect 

 basal disc, the secondary basal cells often sending up erect fila- 

 ments; erect primary filaments 1-4 (usually 2 or 3) from the 

 primary basal cell, 6-14 fx in diameter, often subdichotomous or 

 subtrichotomous at the distal end of the first cell, erect filaments 

 from secondary basal cells 1-4 (when present), commonly more 

 slender, 4-8 ix in diameter, all filaments somewhat rigid below, 

 becoming flexuous above, rather sparingly and irregularly branched, 

 the ramification subdichotomous or distinctly lateral, ultimate 

 branches 3.0-5.5 fx in diameter, mostly elongate-virgate; terminal 

 hairs often present, but rather inconspicuous; cells of filaments 

 cylindric, firm-walled, mostly 3-9 times as long as broad; chromato- 

 phore parietal, usually thin and inconspicuous, single or fragmented, 

 pyrenoid lateral; monoecious; antheridia usually close to the pro- 

 carp, lateral or latero-terminal, solitary or in groups of 2 or 3; 

 cystocarps (frequent) mostly 3-8-spored, carpospores 13-26 /jl 

 X8-i8ai; sporangia (uncommon) monosporous, occurring on 

 sexual plants (sometimes at least), lateral on one-celled pedicels, 

 lateral and sessile, or sometimes terminal on main branches, 

 18-27 /i X 10-18 M- [Plate 15.] 



On Dictyota dichotoma, dredged "in 13H-14 fathoms," Lewis 

 Radcliffe, August 11, 1914; accompanied by Microchaete nana, 

 Streblonema solitarimn, Elachistea stellulata, Phaeostroma piisilliim, 

 Erythrocladia vagabunda, E. recondita, etc. 



Acrochaetium affine is related to A. Hoytii Collins,^ described 

 as an epiphyte on Dictyota dichotoma from the Beaufort region, to 

 A. unipes Bc5rg.,^ described as an epiphyte on Dictyota linearis 

 from St. Croix, and to A. robiistum B0rg.,^ described as an epiphyte 

 on Sargassum viilgare from St. Thomas. It seems possible that a 

 carefully conducted series of cultural experiments, with a rej^ro- 

 duction, if practicable, of the natural growth conditions of these 

 four alleged species, might be able to show that all four represent 



Mihodora 10: 134. 1908. 



2 Mar. Alg. Danish West Indies 2: 35. 1915. 



' Loc. cit. 40. 



