69 
1. Porphyropsis coccinea (J. Ag.). 
Porphyra coccinea J. Agardh, Novitiæ fl. Svec. 1836 p. 6 (without description); J. Areschoug, Phye. Scand. 
mar. 1850 p. 181 tab. I D; J. Agardh (1883) p.56; P. Kuckuck, Bemerk. z. mar. Algenveg. Helgoland II, 
1897, p. 390 fig. 13, 14. 
This pretty little Alga, which has been referred till now to the genus Por- 
phyra, I have met with only at three places in the eastern Kattegat, at 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 chromatophore 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 different; whereas in P. umbilicalis 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 portions 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. The 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-layer 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, the 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 below on the left in 
fig. 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 plan- 
tam nondum lineam altam fere hemisphæricam vidi, nempe lamina marginibus ila 
involuta ut media pars sursum spectaret, apice marginibusque ad ambilum hemi- 
sphærii decumbentibus (Tab. II fig. 41); dum dein eircumeirca increscil, sensim magis 
