48 PROCEEDINGS OF THE AMERICAN ACADEMY 



occupied by a frond of the parasite. Such cases as these, however, 

 are not usual ; ordinarily the host is not so completely covered with 

 the Choreocolax. That the parasite has a deleterious effect on the 

 Polysiphonia is very evident, for the fronds of the latter, on which 

 the Choreocolax is most plentiful, are always paler and less vigorous- 

 looking than the fronds not so affected. The growing tips of the host 

 plant, which usually give every appearance of active growth, are fewer 

 in number, small, and ofteu distorted. Often the terminal branches 

 can be seen to have shrivelled up and rotted away, probably from in- 

 sufficient nourishment. In fronds of Polysiphonia, all stages of this 

 decay may be seen, which varies in intensity according to the 

 amount of Choreocolax on the frond. Some exceptionally strong 

 plants seemed little affected, though considerably attacked by the 

 parasite. 



On examining specimens of Choreocolax PolysiphonicB with a hand 

 lens, they are seen to be usually light-colored masses varying in shape 

 from a flattened hemisphere to almost a sphere. The surface of most 

 of them is smooth and the outline of the frond is regular (Fig. 1), 

 though some are divided unevenly into several lobes (Fig. 2). The 

 cause of this latter condition will be discussed subsequently. The size 

 of these masses that constitute the external portion of the Choreoco- 

 lax is very variable, ranging from small spots that can scarcely be 

 seen, even with a powerful hand lens, to bodies about 2 mm. in diam- 

 eter. The majority of them, however, are not over 1.5 mm. in diam- 

 eter. The small fronds are flattened, becoming more and more nearly 

 spherical as they increase in size and age. It is only the large fronds 

 that are lol)ed in the manner mentioned, the small ones are always 

 quite regular in slripe. The color of the fronds varies from the 

 translucent whitish color of the young ones, to the dirty reddish appear- 

 ance of the adult specimens. Occasionally the latter are dark brown- 

 ish red, though usually they are not very deeply colored, and may 

 sometimes be almost as white as the young fronds. The larger masses 

 of C. Poll/si phonicB are of a tough cartilaginous consistency, fii-mer 

 and more unyielding than the more gelatinous younger fronds. The 

 ap|)earaiice of C Polj/xiplionice is so uniquf, that, togetlier with its 

 habitat, the collector is easily informed of the identity of this rather 

 insignificant-looking alga. 



Before describing the growth and development of the frond, it will 

 be best to explain the structure of the adult plant, wliich cannot be 

 well compared with the conditions presented by other algic. A sec- 

 tion through the frond shows it to be composed for the most part of 



