86 GEVLOX MARINE BIOLOGICAL RI^:PORTS. 



Such algse must, of course, be firmly fixed to their substratum. Whereas the European forms 

 of this type are characterized by smaller or greater adhesive discs, C. Icetevirens has quite a different 

 method of fastening to the rock. In this we find, as in the other Caulerpas, a creeping rhizome, but here 

 much more developed than in the species in general. The assimilation axes, on the other hand, are 

 few and placed at comparatively long intervals, and hence the root system, since it develops numerous 

 fine root branches that fasten themselves to the smallest crevices, corners, or irregularities in the rock, 

 becomes in these plants, in proportion to the assimilation system, much greater than in the other Cauhrpa 

 species. To this must be added — and this seems to me by no means the least characteristic feature of this 

 species — that the assimilation branchlets or pinnules have a strong tendency to grow out into root- 

 forming branches (fig. 19), whereby the whole plant is still more firmly fastened to the rock. That 

 assimilating shoot branches change their character, become procumbent and take root, is, as Webek 

 V. BossE has pointed out (" Monographie des Caulerpes,'' p. 249), not a rare phenomenon. I have given a 

 picture of such a case in C. Fenjusonii (fig. 51 a, b). But in C. Icetevirens it is the branchlets or pinnules 

 (fig. 19, f-i) that grow out into haptera-like rhizomes, and this has become very common in this particular 

 species. As for the shoot system in general, we refer to the description of this species in the special 

 section of the present work. That all this organization is highly advantageous to a species exposed to 

 strong swells, and to the resultant danger of coming loose, is evident ; and C. Icetevirens f . laxa must 

 therefore indisputably be considered as an ecological adaptation to such surroundings. 



Very remarkable is the changed appearance this plant assumes (figs. 21 and 22) when it grows 

 in somewhat deeper localities not so directly exposed to swells. I have called tins biological form /. 

 ccespitosa. It becomes tufted owing to the assimilation branches growing very close together. They 

 are moreover shorter, coarser, and especially more rigid (fig. 22), so that they cannot wave to and fro 

 in the water. To this contributes also the fact that this /. ccespitosa grows squeezed between other 

 tufted algse. Its rhizome and root system are normally developed, not stronger than in the other 

 Caulerpas, and the branchlets, moreover, show no tendency to grow out into root-taking branches. 

 The small, short assimilation-branches are not so pliant in /. ccespitosa as in /. laxa, but more rigid. They 

 are often clavately swollen at the tops, or sometimes flattened. In the last-named case torsion often 

 occurs (fig. 22, b, c), so that the flattened sides are turned up to the light. It is evident that both the 

 clavate form and the torsions of the branchlets produce the same effect, viz., as great a number of chloro- 

 plasts as possible are exposed to the light falling from above. It is interesting that this happeas only 

 in /. ccespitosa, the rigid form with the stiffer branches. The /. laxa, on the other hand, in which the 

 branches wave to and fro, thereby receiving the light from every side, shows no such peculiarities in the 

 organization and position of the branchlets. In this, too, both these forms show differences in their 

 organization that are to be looked upon as ecological adaptations. 



We shall reach a similar conclusion if we compare C. Icetevirens with C. dichotoma (figs. 23, 24). 

 As will be pomted out m the more detailed description of this species, it is closely aUied to C. Icetevirens, 

 from which it differs chiefly in its broad flattened dichotomous assimilation branches, commonly arranged 

 in two rows along the main axis. This organization means a considerable increase in the assimilating 

 surface, but at the same time it entails a number of disadvantages to an alga exposed to strong swells. 

 C. dichotomn is consequently not found in the upper littoral region in places which are so characteristic 

 for C. Icetevirens, but at Weligama it grows at a depth of about 2 metres on sand. The horizontal axis 

 and the root system also corresponds far more in coarseness with the sand Caulerpas tlian with the 

 fine creeping axis of G. Icetevirens. 



Also in C. dichotoma the easy transition from assimilation- branches to haptera is entirely lacking, 

 the reverse of the case in C. Icetevirens, wherein this is so closely connected with its mode of growth. 

 Hence, we see that the characters of these related species are undoubtedly in complete correspondence 

 with their mode of growth and with the closely connected surroundings. 



