endogenous branches may reach a considerable length. Secondary axillary shoots 
developed from the basal cell of trichoblasts also frequently occur, but these shoots 
Fig. 393. 
Polysiphonia nigrescens. 
Endogenous adventitious 
shoot at the limit between 
the second and the third 
joint of the branch. Small 
cortical cells have been 
cut off from the lower end 
of the pericentral cells. 
220 :1. 
usually reach only a small size (K. R. 1884 fig. 29); they some- 
times arise before the trichoblast has been shed (fig. 395 A). 
The trichoblasts show the usual structure; they have at least 
three generations of branchlets. The older cells contain a number 
of nuclei each (fig. 395 B). In specimens collected in April the 
trichoblasts had in a living stage a feeble rose tinge due to 
the cell sap, but the small round chromatophores were also 
feebly coloured. Later in the year the cell sap may have a 
brownish tinge. 
The first joint of the branches is short and has only peri- 
central cells on its outer side, in a number of 4—6, the second 
‘joint of the branch being at the base in connection with the 
following joint in the mother axis. It may happen, however, 
that the first transversal wall of the branch does not reach the 
mother axis, but the first joint of the branch is at all events 
shorter than the following ones (fig. 394 A). A peculiar case 
is shown in fig. 394 B, where the third joint bears at the back 
the basal cell of a trichoblast whereafter follows a bifurcation, the two branches 
being of equal strength and diverging equally from the original direction of the 
axis. This must probably be because the apical cell, after having produced a tricho- 
blast-bearing segment, has been divided 
by a vertical wall in two equal parts, 
each giving rise to a branch, a true 
dichotomy thus occurring here. 
In the upper part of the plants the 
first lateral organ on the branches usually 
occurs on the 3rd to the 5th joint, in 
the season of vegetation. The basal joint 
of the trichoblasts may sometimes pro- 
duce pericentral cells, as if it were the 
basal joint of a branch (fig. 395 B). These 
trichoblasts must be apprehended as 
transitional forms approaching to the 
branches. A further transitional stage is 
shown in fig. 295C, where the two lower- 
most joints are provided with pericentral 
cells and the upper of these has produced 
a tetrasporangium, while the upper part 
IE 
Fig. 394. 
A, pseudodichotomy; the first 
Polysiphonia nigrescens. 
joint of the branch (to the left) is long, with pericentral 
cells all round, though shorter than the following joints. 
50:1. B, portion of young plant; probably true dicho- 
tomy (see text). 
of the lateral organ has the character of a trichoblast, though it is unbranched. In 
winter (January) the plants as a rule bear no trichoblasts (fig. 392). The growth 
