MARINE Al^GM OF BEAUFORT, N. C. 471 



Very abundant on Dictyota dichotoma on Fort Macon jetties, Beaufort, N. C., less abundant on 

 Dictyota in harbor, usually unmixed with other algae, summer -and autumn. 



Endemic. 



This species appears to be related to A . dufourii on the one side and to A . affine on the other. In 

 fact, these three species seem to form an intergrading group, so that distinctions are frequently very 

 difficult. From A. dufourii it is distinguished by its usually larger size, larger, sometimes slightly 

 embedded basal cell, more abundant branching with consequent denser habit, and its usually more 

 elongated branches tapering toward the apices. The germinating spore seems to not merely remain 

 distinct throughout the life of the plant, but to increase to many times its original size, and may send up 

 as many as four erect filaments. It is distinguished from A. affine by its smaller size, its smaller and 

 shorter cells, its more nearly spherical and more superficial basal cell, the absence of horizontal filaments, 

 the abundance of sporangia, and the great scarcity of cystocarps. The basal cell usually remains 

 unchanged except for its increase in size, and forms, at most, a few secondary basal cells which do not 

 give rise to upright filaments. The general habit resembles A. corymbiferum but it is readily distin- 

 guished from that species by the differences in the basal portions of the plants and in the formation of the 

 organs of reproduction. Its habit is sometimes very dense . 



Small plants of A . hoytii are especially difficult to distinguish from A . dufourii since they are often 

 sparsely branched and do not bear elongated, tapering branches. With' such plants the principal 

 distinguishing character is the size of the basal cell, but even with this it is not always easy to determine 

 to which of these species a given plant should be referred. 



4. Acrochaetium affine Howe and Hoyt. PI. CXIX. 



A cr ochtetium affine, Howe and Hoyt, 1916, p. 118, pi. 15. 



Plants i to 3.5 mm. tall; basal cell (original spore) subglobose or ellipsoid, mostly 14 to 26 mic. in 

 diameter, finally becoming subpyriform and 20 to 33 mic. high through the development of a subcylindric 

 obtuse or truncate foot penetrating the host for about 10 to 24 mic., 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 to 5 cells long, these very rarely forming a small imperfect basal 

 disk, the secondary basal cells often sending up erect filaments; erect primary filaments i to 4 (usually 

 2 to 3) from the primary basal cell, 6 to 14 mic. in diameter, often subdichotomous or subtrichotomous at 

 the distal end of the first cell, erect filaments from secondary basal cells i to 4 (when present), commonly 

 more slender, 4 to 8 mic. in diameter, all filaments somewhat rigid below, becoming flexuous above, 

 rather sparingly and irregularly branched, the branching subdichotomous or distinctly lateral, ultimate 

 branches 3 to 5.5 mic. in diameter, mostly elongate-virgate, terminal hairs often present, but rather 

 inconspicuous; cells of filaments cylindric, firm-walled, mostly 3 to 9 times as long as broad; sporangia 

 uncommon, lateral on one-celled pedicels, lateral and sessile, or sometimes terminal on main branches, 

 18 to 27 mic. by 10 to 18 mic. ; antheridia usually close to the procarp, lateral or somewhat terminal, 

 solitary or in groups of 2 to 3; cystocarps abundant, mostly 3 to 8 spored, carpospores 13 to 26 mic. by 

 8 to 18 mic. ; antheridia, cystocarps, and (sometimes at least) sporangia occurring on the same individual. 



Abundant on Dictyota dichotoma and occasional on Spyridia filamentosa and other hosts dredged 

 from the coral reef offshore from Beaufort, N. C., August, 1914. 



Endemic. 



This species most nearly resembles A. hoytii, which is borne on the same host in Beaufort Harbor. 

 From this it differs in its larger size, its larger and longer cells, its more elongated and more embedded 

 basal cell, its occasional formation of horizontal filaments, the infrequent formation of sporangia, and 

 the relatively abundant cystocarps produced on the same plants. Its general habit resembles A. 

 coymbiferum, from which it is distinguished by its larger, more persistent, partially embedded basal 

 cell, the upright filaments often arising entirely from this, by the less abundant cystocarps, these, the 

 antheridia, and the sporangia being borne on the same plants, and by the fact that the horizontal fila- 

 ments, when present, are mostly external. From A. dufourii it is distinguished by its larger size, its 

 larger, partially embedded basal cell, its more abundant branching, the branches tapering toward the 

 apices, and by its fairly abundant production of cystocarps. 



