176 
hairs are sometimes found given off from intercalary cells in the vertical filaments. 
The cells producing them are usually more or less projecting, but the hairs are 
feebly developed; they do not ordinarily reach the surface of the frond, and soon 
decay. Once only have I seen a few such hairs projecting 
over the surface, as in fig. 94 E where the hair, however, 
is terminal on a one-celled branchlet!, — The crusts may 
certainly reach an age of more than one year. In crusts 
growing on stems of Laminaria hyperborea a stratification 
is often visible which seems to be due to the cessation of 
the growth in winter; in the part of the crust beneath the 
limitating line empty or abortive fructifications may be 
Fig. 93. found, while new fructifications have not yet been produ- 
Petrocelis Hennedyi, from the 0 
Limfjord (ZY), showing peculiar Ced in the upper part of the frond apparently formed after 
ramifications of vertical fila- the hibernal rest. 
ments. 390:1. 
Characteristic of the genus are the intercalary spor- 
angia. In this species there are as a rule several consecutively in the same fila- 
ment, in Danish specimens frequently six at least in a row, but there may be up 
to nine. The row is never interrupted by sterile cells. The sporangia are situated 
in the upper part of the vertical filaments, only the (1—) 2—5 uppermost cells 
being sterile. The sporangiferous vertical filaments are usually unbranched, but 
sometimes a branch is given off, rarely from the articles transformed into sporangia, 
more frequently from the cell subjacent to the sporangial series (fig. 95). The spor- 
angia are first divided by an inclined transverse wall and then by two walls per- 
pendicular to the wall first formed. The latter are frequently parallel, but the lines 
of intersection with the transverse wall do not coincide. These seriate sporangia 
are of about the same height as breadth, 14—17 y 
broad, 16—23 » high. 
In most of the crusts only seriate sporangia 
are present; but in some cases the sporangia were 
single or at most two in a series. These sporangia 
are more lengthened than the seriate ones. A transi- 
tional case is shown in fig. 95 D, where the series 
contains only two sporangia. But in fig. 95 G and 
H single, terminal or subterminal sporangia are 
A represented. In fig. 95 H the sporangium seems to 
À be terminal, but I cannot assert that there has not 
aie Gi : been one or more sterile cells which may be de: 
Petrocelis Hennedyi. Vertical filaments with cayed DL possibly removed by the preparation. 
hyaline hairs. A—C from Begtrup Vig; in Similar sporangia were found in a thin crust with 
C the hairs have been thrown off, the 
chromatophore of the cells is visible. DE the ends of the filaments truncate; fig. 96 shows 
from Hellebæk, E after a living plant with 
a well developed hair at the top of a uni- 7 Comp. L. KoLDErup ROSENVINGE, Hyaline hairs (Biol. 
cellular branchlet. A—D, 400:1; E, c.200:1. Arbejder, tilegn. E: Warming, 1911, p. 206). 
Fs 
