BOT.-VOL. II.] HUS-PORPHYRA. 183 



The value of the prothalloid base lies evidently in the 

 power to form a large number of fronds rapidly, which in 

 the production of new fronds in case of accident is clearly 

 of great importance. 



As far as the author is aware, P. naiadum has never 

 been found growing on any substratum other than eel-grass, 

 nor has a cushion-shaped base such as here described ever 

 been found in any other species of Porphyra. The nearest 

 approach to such a description is that of the base of P. 

 coccinea J. Ag., such as is found in Agardh's "Till 

 Algernes Systematik" VI (1882). But judging from this 

 account, the base is hollow, being formed by the involution 

 of the edges of the young frond. When the frond grows 

 older the base finally flattens out. 



It is worthy of note, that in connection with P. coccinea 

 Agardh mentions a Porphyra occurring in large numbers 

 on the Pacific Coast; it grows on seaweeds ( !), and judging 

 from the description given might possibly be P. naiadum. 



The color of the fronds of the different species of Por- 

 fhyra is such as to lead one to place the genus among the 

 Floridese. But the color is far from being constant. A 

 hundred different shades may be met with, for even the 

 color of the different fronds belonging to one species 

 varies; so that an attempt to describe a species by the 

 color would be futile. While the color of one species (P. 

 tenuissima) is, as a rule, a delicate pink, others are a bright 

 red or even crimson, as P. abyssicola. P. laciniata exhibits 

 a decidedly purple color, while P. perforata appears mostly 

 yellow-brown. The frond of P. variegata is crimson when 

 sterile, while when fruiting it acquires the beautiful varie- 

 gated appearance indicated by its name. 



An important fact is that the color of herbarium specimens 

 generally changes. This was most notable in P. perforata. 

 Specimens which when collected had a yellow-brown tint 

 generally became a deep blue-purple. Some of the fronds 

 of P. nereocystis underwent a change in the herbarium, 

 while others retained the original dull brown-red color. 



Especially did specimens which were rough-dried and 

 afterwards soaked in fresh or salt water for mounting 



