152 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



forms the clava may occupy from one-tenth to three-fourths of 

 the total length, the clava and stipe may be plainly distinct, or 

 may pass into each other imperceptibly. The plants are mostly 

 gregarious, often growing in abundance over long stretches of 

 shore between tide marks, either alone or in company with other 

 small algae ; though comparison of specimens collected at dif- 

 ferent times and places will show many gradations of form, it is 

 usually found that all the plants of one collecting are uniform 

 in character. Quite a number of species have been described, 

 but it has seemed best here to recognize only three, including 

 others under them as forms. 



KEY TO THE SPECIES OF 

 i. Growing among the tissues of other algae. i. C. Petrocelidis. 



i. Free. 2. 



2. Clava ovoid, much thicker than the stipe. 2. C. gregarium. 

 2. Clava narrowly clavate, not much thicker than the stipe. 



3. C. p n si 1 1 inn. 



1. C. PETROCELIDIS Kuckuck, 1894, p. 259, fig. 27. Fronds 

 endophytic, in tissue of Petrocelis ; clava ovoid or obovoid, 

 65-90X20-30 /u, ; stipe very slender, usually terminating below 

 in a point. Me. to Mass. Northern Europe. 



The cells are developed among the vertical filaments of the 

 host, and can be detected only by microscopic examination. 

 The endophytic habit of this species renders the stipe unneces- 

 sary, and it has become little more than a rudiment. 



2. C. GREGARIUM A. Braun, 1855, p. 20, PL I ; Farlow, 

 i88i,p. 58; P. B. -A., No. 165. Clava ovoid, 250-500X65- 100 /x, 

 sharply distinguished from the stipe, which varies from 600- 

 1000 /* in length, and 20-30 ^ in thickness. Occurs usually in 

 company with Calothrix, etc., on rocks and shells, along the 

 New England coast ; rarely found unmixed, or forming so large 

 a proportion of the mixture as to be noticeable except in micro- 

 scopic examination. Fig. 37. Me. to N. Y. Europe. 



Forma intermedium (Foslie) nov. comb. ; C. intermedium 

 Foslie, 1887, p. 193, PI. II, figs. 1-12; Wittr. and Nordst., 

 Alg. Exsicc., No. 954. Stipe 170-250X25-40^ ; clava 150-300 >< 

 55- no fji. Me. Northern Europe. 



An extreme form, with much swollen, sometimes almost 

 spherical clava, and short, stout stipe. It has been found 

 among Calothrix scopidorum on islands off Portland harbor, 

 Maine. 



