408 
where erect shoots may be entirely wanting. The procumbent and erect shoots issuing 
from a procumbent one are always of endogenous origin, budding from the central 
cell, usually very near to the rhizoids (fig. 343). Endogenous branches also fre- 
quently arise from the lower part of the erect shoots (fig. 342). The rhizoids which 
always arise from the pericentral cells, except the first rhizoid of the sporeling, 
sometimes obviously testify to a shortening, the cuticle being transversely wrinkled 
(fig. 343). 
FALKENBERG has maintained that P. urceolala lacks trichoblasts (1901 p. 151). 
As shown by me (1903, p. 450), this may be true but only in autumn and winter, 
when the development of the plant has ceased, while the specimens collected in the 
months of March to June are normally provided with trichoblasts, and these organs 
may still be present in July and August. In the creeping branches, however, they 
Fig. 343. 
Polysiphonia urceolata. Procumbent branch with rhizoids and endogenous branches. 50 : 1. 
are always wanting. The trichoblasts show the typical structure, having the first 
branchlet always on the right side (fig. 346); their cells contain one nucleus and small 
plastids which are usually colourless but may be feebly rose-coloured in early spring 
or in shaded localities. They are arranged in a spiral turning to the left! but are 
usually separated from each other by more than one joint. The branches occur in 
the spirals in the place of the trichoblasts, but the relation of frequency of the two 
kinds of organs to each other is very variable. The erect shoots often over a long 
stretch only bear branches arranged in a spiral with a divergence of '/ı separated from 
each other by 3 to 5 joints, and the trichoblasts appear only at the upper end of 
the shoot intermingled with branches; but in other cases the trichoblasts appear 
already in the lower part of the shoots. At the upper end of the shoots in partic- 
ular of the fertile male and female plants, the trichoblasts may be more densely 
placed, each joint bearing one trichoblast. The erect filaments issuing from the 
creeping ones are often without primary lateral organs over a long stretch from the 
base, but endogenous adventitious shoots may frequently occur here (fig. 342). 
Trichoblasts have been met with in specimens collected near land and in spec- 
imens from greater depths as well (f. inst. bM, south of Hveen Su 22,5 m). They 
are shed in summer, when the growth is sisted. This usually takes place in June 
or July, but specimens in vegetative development may still be met with in August; 
these specimens seem, however, always to be young plants produced from spores 
germinated in the same season. 
* A rare exception is shown in fig. 341 A, where the spiral turns to the right. 
