69 



1. Porphyropsis coccinea (J. Ag.). 



Porphi/ra cocciiiea .1. Agardli, Novitia' 11. Svec. 1836 p. (i (without description); .1. Aresclioug, Pliyc. Scaiid. 

 mar. 1850 p. 181 tab. ID; J. Agardh (1883) p. fjfj; P. KiickiicU, Bemerk. z. mar. Algenveg. Heigolaiul II, 

 1897, p. 390 fig. 13, H. 



This pretty little Alga, wiiich has heen referred till now lo the genus Por- 

 phyra, I have met with only al three places in the eastern Kattegat, al the two 

 only in extremely small quantity. As its mode of fructification has been hitherto 

 unknown, its systematic position has remained uncertain, as pointed out by Kuckuck, 

 who showed that the chromalophore has no central pyrenoid as in the other spe- 

 cies of Porphyra but that it forms a much divided parietal plate. It will be seen 

 from the following that this plant also in other respects differs so much from the 

 typical species of Porphyra, that it must be removed from this genus. Thus the 

 development of the frond is quite ditl'erent; whereas in P. iimbilicalis this begins 

 as a filament which early becomes leaf-like, being divided by longitudinal walls, 

 in Porphyropsis coccinea the frond is at first cushion-like, parenchymatous and 

 composed of more than one layer of cells. The frond increases in height and 

 becomes globular and vesicular. Such a condition is to be seen in Fig. 9 A. As 

 this and other similar plants were growing together with more advanced stages of 

 this species and as they much resembled the lower, basal ])ortions of the latter, I 

 conclude that they belong really to the same species. The plant figured is nearly 

 hemispherical with a lobed plane of attachment, in the margin of which the cells 

 are somewhat elongated. Tlie upper part of the frond consists of a layer of cells 

 which are actively dividing by anticlinal walls; the growth caused by these divi- 

 sions has caused a separation of this cell-laj^er from the cells lying within, and the 

 continued growth must necessarily cause the plant to become more and more ve- 

 sicular. A rupture of the vesicle must, however, take place at an early period, for 

 small individuals occur with an irregularly lobed monostromatic frond tapering 

 downwards and ending in a cushion-like, basal disc resembling the under part of 

 fig. 9 A. In consequence of this development the young frond is usually more or 

 less cup-shaped; in particular, tlie margins immediately above the basal cushion are 

 most frequently bent inwards to the same side. The expanded frond projects from 

 the one side of the basal cushion, the greater part of which is situated at the hol- 

 low side of the young frond. On the side of the cushion opposite to the frond are 

 often to be seen irregular projections representing the lower border of the split by 

 which the monostromatic frond has arisen. The lap visible tielow on the left in 

 lig. 9 C belongs undoubtedly to this category. The formation of the split itself I 

 have unfortunately not observed; probably a transverse split is formed on the one 

 side of the vesicular frond. The development here described is not entirely un- 

 known; J. Agardh (1883 p. 56) describes the young plants thus: "Hoc modo i)lan- 

 tam nondum lineam altam fere hemisphtericam vidi, nempe lamina marginibus ila 

 involula ul media pars sursum speclaret, apice marginibusque ad ambiluin hemi- 

 sphserii decumbentibus (Tab. II fig. 41); duni dein circumcirca increscit, sensim magis 



