Halecium minutum Broch 1903. 
While this species usually has a creeping rhizocaulus from 
which small, simple, slightly branched stems issue, some specimens 
from the Tjalfe” Expedition have a solid, compound stem with 
Several branches. I have previously (in the chapter "stolonisation” 
in Rep. on the Hydroids from NE-Greenland, 1911) called attention 
to the transition existing between creeping and erect stems. A 
"stem” issuing from a common creeping rhizocaulus is homologous 
With a branch of an erect, monosiphonie hydrocaulus, and, similarly 
the single tubes of a polysiphonic stem, such as in Lafoéa fruticosa 
for instance, have to be considered as a collection of rhizocauli growing 
on each other and sending out branches, homologous with the erect 
stems from a common rhizocaulus. Each tube of the polysiphonic 
stem may leave the stem and attach itself to objects (stolonisation) 
transforming itself into a common rhizocaulus from which new 
Sstems” (== branches) may grow out. 
Now the fact is, that one and the same species has usually 
one mode of growth, either creeping stolon, on which the individuals 
åre placed without forming any sort of stems, or creeping rhizocaulus 
with simple erect stems, such as is usually the case in /. minutum ; 
or a compound stem more or less differentiated. We know, however, 
Several examples of .colonies with another shape than the ordinary, 
not merely young colonies of polysiphonie species having not yet 
developed compound stems, but also well-grown colonies differing 
from the ordinary mode of growth of the species. In the above 
named paper I have mentioned some cases of Grammaria serpens 
With erect, branched stems. In Lafota dumosa we know as well 
Creeping forms very much alike G. serpens, as erect forms either 
with simple, irregularly branched stems or with polysiphonic stems 
with a certain regularity in the mode of branching, forma triaxi- 
alis Lev. Even in Campanularia verticillata, which seems to be 
rather highly developed as regards the structure of the colony, I 
have seen single hydrothecæ issuing from the creeping root-tubes 
of the colony. A good example of a species with different modes 
