358 f- Kramp. 



as of importance in the vegetative propagation bnt in another \\ay : 

 "Einmal dienen die Ranken ganz wie die Luftwurzehi der Pflanzen 

 zur besseren Befestigung des Stockes, das andere Mal zur ungesclecht- 

 lichen Vermehrung wie die Pflanzensprösslinge", in that long tendrils 

 can grow round stones and send up new stems. 



A dense matting of Sertiilarella or Lafoëa is "as thick as weavers" 

 and the union helps here as everywhere both the single unit of the 

 society and the society as a whole; it is very capable of resistance 

 against forcible encroachment and is able to hold its own, and the 

 colonies will continually grow larger and denser; the bridges and 

 the tendrils will certainly also serve to keep the branches at a suit- 

 able distance and prevent them from rubbing too much against 

 each other; if the branches were allowed to do so, they would in 

 the first place become worn, and secondly, no hydranths would 

 thrive except on the outermost branches of the colon}^; between the 

 dense branches the supply of water Avould be insufficient and the 

 hydranths would incessantly be driven into their hydrothecae by 

 the rough touch of the neighbouring branches, when the waves set 

 them in motion. The bridges thus serve not only to keep the 

 branches together but also to keep them apart. 



In the polysiphonic hydroids the single tubes are by their nature 

 intended to grow on each other; it is not remarkable, therefore, that 

 a tube can also attach itself to a foreign object; but, as above-men- 

 tioned, hydranthless threads seem to be developed even here, with 

 the particular purpose of forming a bridge between two branches. 

 The stolonized branch of Haleciiim labrosum figured (Plate XXI, fig. 

 2) seems also to be intended to become a stolon. That the bridges 

 in Lafoëa are most numerous in dense colonies is easily understood; 

 they might be formed from ordinary branches and these in a dense 

 colony have plenty of opportunity of coming into contact with one 

 another. But in Sertiilarella this quite mechanical explanation is not 

 sufficient. 



In Sertiilarella the connection alwaj's occurs at specially trans- 

 formed ends of branches, being wrinkled and hydranthless for some 

 (shorter or longer) distance within the connecting point. That these 

 tendrils are only or specially found on large, dense colonies seems 

 to show, that the cause of their formation make be looked for in 

 the shaking, which is produced at the ends of the young branches 

 by frequent contact with the neighbouring branches during the 

 movements of the colony caused by the action of the waves. 



In this connection I may also mention, that species with filiform, 

 creeping hydrocaulus may occur with free, erect stems; not only 



