568 Howe : Phycological studies 



Rhizoidal filaments often have such a character but Kutzing states 

 that the figured filament came " aus dem Phyllom." 



Avrainvillea nigricans and A. Mazei, as we interpret them, are 

 best distinguished by the character of the filaments of the flabel- 

 lum, those of A. nigricans being moniliform and those of A. Mazei 

 being cylindrical with an abrupt constriction at the base of each 

 branch. The flabellum in A. Mazei tends to be more diffuse, 

 fluffy, and irregular, and it is often greener. In three cases, we 

 have found the two growing side by side and perfectly distinct in 

 form, color, and in the microscopic characters of the threads, yet 

 elsewhere specimens have sometimes been found which seem to 

 hold a rather doubtful intermediate position. In one case (Ber- 

 muda, no. lop) filaments from two flabella springing from a single 

 rhizome have different characters, those from the one being clearly 

 of the Mazei type while those from the other make a close ap- 

 proach to the regularly moniliform condition of A. nigricans. 

 The fact that A. nigricans and A. Mazei have been found wholly 

 distinct when growing together under apparently the same condi- 

 tions leads to the opinion that they should be considered separate 

 species in spite of some present difficulties in the way of always 

 recognizing them. Each of the two presents wide variations in 

 form, size and color. What we believe to be a low-littoral or 

 shallow-water condition of Avrainvillea Mazei forms greenish- 

 brown, caespitose masses near low-water mark on exposed rocks, 

 and has finger-shaped or round-capitate lobes, not developing a 

 flabellum unless it descends a decimeter or more below the low- 

 tide line. Among the forms that we are at present identifying 

 with A. nigricans, one extreme is represented by plants with a 

 suborbicular flabellum (reniform-cordate when young), reaching a 

 width of 25 cm., supported by a cylindrical stipe, which has a 

 maximum length, so far as observed, of 16 cm., this springing 

 from a strongly developed rhizome ; the other extreme has a 

 cuneiform flabellum, sometimes no more than 1—2 cm. wide, taper- 

 ing gradually to a flattened scarcely recognizable stipe, with 

 rhizome poorly developed. Between these two extremes there 

 seems to be a nearly perfect scries of intermediates, but perhaps 

 further familiarity with the genus, particularly with living speci- 

 mens, will result in the recognition of some satisfactory basis for 

 specific distinctions. 



