BoT.-Voi-. II.] HUS—PORPHYRA. 203 



the violence of the waves they disappear in the fall, some- 

 thing to which the dry north winds which frequently occur in 

 California during the latter part of the year contribute not 

 a little. The result of this is that in December and January 

 the fronds are found in sheltered places only. 



P. perforata occurs throughout the litoral zone and in the 

 upper part of the sublitoral zone. There is some difference 

 in form between the plants of the upper part of the litoral 

 zone and those of the sublitoral zone. While the former, 

 which the writer considers typical, are lanceolate, with a 

 cordate base and a frond which is but slightly perforate, the 

 latter are far more irregular, being much lobed and laciniate, 

 with an umbilicate base, and are much perforate. They 

 also seem of finer texture and are as a rule much thinner. 

 This, however, is not always the case. The author has 

 collected specimens in the sublitoral zone which in the 

 sporocarpic portion of the frond measured iio/A,a thickness 

 which corresponds to the average measurement of the sporo- 

 carpic parts of the fronds of the litoral zone. The differ- 

 ence in thickness seems to lie chiefly in the jelly, the latter, 

 in the fronds of the litoral zone being as a rule more abun- 

 dant than in the fronds of the sublitoral zone. 



The specimens of P. perforata found in the sublitoral 

 zone also possess a color different from that of the fronds 

 of the litoral zone. While the latter are a gray- to brown- 

 violet, the former are altogether devoid of a violet shade 

 and appear a gray- or yellow-brown. This difference in 

 color is very striking, and at first led to many conjectures. 

 But in the light of the fact that herbarium specimens after 

 having been preserved for six months or more begin to take 

 a violet hue, a color, the various shades of which are often 

 characteristic of the various species to which the genus 

 owes its name, and chiefly its inclusion among the Rhodo- 

 phyce^, it seems but reasonable to suppose that the deeper 

 violet color of the specimens of Porphyra perforata found 

 in the litoral zone is due to the action of the air. What 

 the other causes for the difference may be has not yet been 

 solved. Perhaps the slug, which in all probability causes 



