Box.— Vol. II.] HUS—PORPHYRA. 213 



occurring on Zostera usually attach themselves to the edges 

 of the blade, forming a broad fringe. 



In the spring of 1898, Dr. Setchell called the attention of 

 the author to some plants of Phyllospadix, the leaves of 

 which were densely covered by numerous small, reddish- 

 brown, cushion-shaped growths, which he suspected to 

 stand in some relation to P. naiadum. On examination, 

 these cushions proved to consist of a number of angular cells 

 (PL XXI, fig. 19), the outer layers of which contained chro- 

 matophores, which were deeply lobed, somewhat after a stel- 

 late fashion, resembling those described by Schmitz (1882) 

 for Hehninthocladia purpurea. Each cell of the layer 

 adjacent to the substratum possessed a short rhizoid, which 

 apparently attached itself to the cuticle of the host-plant. 

 In the beginning of February, these cushions begin to show 

 short hair-like projections. These projections are composed 

 of cells placed in a single narrow layer. The youngest of 

 them consist of but a few cells placed in a single row. 

 Older specimens show that these cells divide in two direc- 

 tions, giving rise to a monostromatic frond which proves to 

 be Z'. naiadum (PI. XXI, fig. 22). 



The cells of the lower part of the frond, unlike those at 

 the base of fronds of other species of Porphyra, do not 

 produce hypha-like projections. Even in the oldest plants 

 no sign of this was to be found. This prothalloid base is 

 different from the bases of all known species of Porphyra, 

 as described by Berthold, Thuret, and others, with the 

 exception, perhaps, of one described by J. G. Agardh (1882) 

 under the name P. coccinea. 



The size of the frond varies somewhat. The young 

 fronds are obovate, measuring about one centimeter across; 

 but the frond gradually broadens and lengthens, finally 

 assuming an oblanceolate shape, being from four to ten 

 centimeters long and two or three centimeters broad. There 

 is a considerable difference in size and color between speci- 

 mens growing in sheltered places and those growing in the 

 open. In fact, we may distinguish between two forms — a, 

 minor and b, major. Under the first, we understand the 



