BOT.— Vol. II.] H'JS ^rORPHYRA. 185 



Kjellman applies the name Difloderma to all distromatic 

 species, but the above mentioned results lead the writer to 

 agree with Rosenvinge in applying the name Por-phyra to 

 all members of the genus, while retaining Diploderina 

 ( Wildcmania de Toni) as a subgeneric name for the di- 

 stromatic fronds, the more so as in habit and external char- 

 acter the monostromatic and distromatic species agree in all 

 respects. 



Two sources of confusion in determining the number of 

 layers in the frond exist. The first is the age of the frond, 

 the second, the formation of reproductive cells. Young 

 fronds of distromatic species are frequently monostromatic. 

 This monostromatic character persists in the vegetative por- 

 tion of the frond even after the fruit has been formed (P. 

 abyssicola) (Rosenvinge, 1893). The same results were 

 obtained by the author in his observations on P. abyssicola, 

 but he cannot confirm Rosenvinge's statement, that in the 

 distromatic forms the inferior portion of the thallus is com- 

 posed of a single layer of cells. "Dans les formes distro- 

 matiques, du reste, la partie inferieure du thalle est composee 

 d'une seule assise de cellules" (Rosenvinge, 1893, p. 84). 

 On the contrary, if we do not consider those oiP. abyssicola, 

 but few, if any, distromatic specimens were found which 

 were monostromatic at the base. As a rule, whenever a 

 frond of a distromatic species was partly monostromatic, the 

 monostromatic portion was found in the region of the tip at 

 the edge. 



Monostromatic species practically become distromatic as 

 soon as the reproductive bodies begin to form. The second 

 division of either the antheridium or sporocarp-mother-cells 

 takes place in a direction parallel to the surface of the 

 frond, and in this manner gives rise to two layers of cells 

 which are often difficult to distinguish from purely vegetative 

 cells; so that in deciding their nature, the cells of the sur- 

 rounding tissue must be taken into account. 



The thickness of the fronds of the various species of 

 Porphyra is more or less variable, and though not an abso- 

 lutely specific character, taken in conjunction with other 



