Report on the Hydroids. 357 



keep the much ramified and entangled colonies togetlier to a 

 coherent web. 



\n Sertnlarelhi triciispidata I have seen a great many examples 

 of stolonisation. In this species the stem and branches are never 

 compound ; we might imagine beforehand tlierefore, that the erect 

 branches had no tendency to form stolons; but in reality we very 

 often find that the end of a branch has continued its growth with- 

 out forming hydranths and has developed into a long, WTinkled, 

 crooked thread. If the end of such a thread comes into contact 

 with another branch of the colony, it fastens itself on this, twines 

 round it like a tendril (Plate XX, fig. 6) and may leave it again to 

 grow on as a normal hydrotheca-bearing branch. If a stolonized 

 end of a branch comes into contact with a solid object, e. g, a stone 

 (Plate XX, fig. 5), it attaches itself and creeps across the support like 

 an ordinary stolon, which may ramif\' and send out new hydro- 

 cauli. Plate XX, fig. 7 shows a tendril, which has given up seeking 

 for a connecting point and has begun to form hydranths once more; 

 nor is it rare, on an ordinary branch, to see a long, wrinkled piece 

 without hydrothecae, evidently corresponding to a tendril, which has 

 not found a support and has grown on in the normal way (cf. text- 

 fig. 16 in Hartlauh (24)). 



As to the importance of the phenomena of stolonisation mentioned 

 and the causes of their formation, I shall only make the following 

 remarks. According to Hartlaub (24), the stolonisation has 3 

 important functions: The stolons keep the branches together, anchor 

 the colony and spread the species, in that detached pieces can cert- 

 ainly attach themselves at some other places. — The attachment of 

 stolonized branches to solid objects is obviously of advantage in 

 giving the colony new holds. The "bridges" (of the polysiphonic 

 species) and the "tendrils" occur in great abundance on large dense 

 colonies. They give the colony a considerable solidity, so that it is 

 difficult to tear it in pieces; even if a branch is broken at its base, 

 yet it would remain hanging by the tendrils and thus escape the 

 danger of being carried away by currents and the waves and per- 

 haps being thrown up on the land. The tendrils will thus rather 

 counteract a vegetative distribution, but it must be admitted that 

 the power to send out stolons may possibly be a benefit to a de- 

 tached branch, by fastening it when it again comes under quiet 

 conditions, though it is a question wdiether the new stolons would 

 not rather in such cases develop from the basal surface than from 

 the ends of the branches. 



B. v. Campenhausen, (18) p. 306, also considers the stolonisation 



26* 



