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



2. Strictly epiphytic. 4. U. prostrata. 



2. Penetrating the host more or less. 3. 



3. Gelatinous, up to 75 M thick, not confluent. 2. U.fucicola. 



3. Not gelatinous, up to 250 /u thick, confluent. i. U. conflucns. 



1. U. CONFLUENS Rosenvinge, 1893, p. 924, fig. 39. Form- 

 ing green, confluent incrustations on old stipes of Laminaria 

 longicruris ; when mature, to 250 /JL thick, smooth, composed 

 of more or less regular, closely united, vertical filaments, 

 diverging towards the margin; cells 10-12 yu diam., 2-4 diam. 

 long, the disk- or cap-shaped chromatophore at the top ; dissepi- 

 ments horizontal or oblique, somewhat curved upward ; terminal 

 cells of the same size and form as the others, but with rounded 

 top and richer contents : sporangia formed from the superficial 

 cells, little changed in form or size, but with tip more acute ; 

 zoospores 30-40 in a cell, escaping by a terminal opening. 

 Greenland. Northern Europe. 



At first this plant is mouostromatic, resembling a Prinxshcimiti, 

 and even in this state produces spores. It continues to increase 

 in thickness, and empty sporangial cells may be found quite a 

 distance below the surface ; from the lower surface short fila- 

 ments penetrate the host plant to a greater or less depth. 



2. U. FUCICOLA Rosenvinge, 1893, p. 926, fig. 40 ; Olt- 

 manns, 1894, p. 211, PL VII, figs. 11-13. Frond pulvinate or 

 hemispherical, to 75 /j. thick, somewhat gelatinous, composed of 

 oblong cells arranged in more or less distinctly radiating series ; 

 cells 5-7 fj. diam., 3-5 diam. long, wall not sharply marked off 

 from the general gelatinous coating; chromatophore parietal, 

 occupying the middle part of the cell ; all cells, except perhaps 

 the basal layer, developing into sporangia, which swell to twice 

 the size of the vegetative cells, and are pushed out from among 

 them ; zoospores 6-10 in a sporangium. On old plants of FKCKS. 

 Greenland. Northern Europe. 



Quite different both in habit and structure from U. conHucns, 

 forming smaller, not confluent, more gelatinous fronds, with 

 smaller cells, and less sharply differentiated sporangial layer. 

 It penetrates the host plant, but not to such an extent as U. 

 con flue ns. 



3. V . LENS Crouan, 1859, p. 288, PI. XXII, fig. E. Fronds 

 orbicular, 1-3 mm. diam., cells 15-20 p. diam. in center of frond, 

 near the margin 10-15X20-30^; frond usually not over three 

 layers thick in the center of the frond. Fig. 102. North 

 Carolina, on stones and shells. Europe. 



