230 



Siphonales 



both the rhizome and the root-like holdfasts varies much in the different 

 species, depending upon the habit of the plant and the nature of its 

 environment. The necessary mechanical support for the thallus is not 

 obtained by the interlacing of branches or by calcification, as in so many of 

 the Siphonales, but mostly by the great turgidity of the coenocyte. A dense 

 lattice-work of internal trabeculaa or cross-beams traverse the lumen of the 

 coenocyte from wall to wall (fig. 151) and prevent any over-distention or 

 possible bursting. There is no cellular structure in the thallus and the 

 plant is but a hollow mockery of the higher type which it simulates. 



The cell- wall is thick and distinctly lamellose, with an outermost layer which gives 

 rise to the trabeculse. The transverse trabeculse are strengthened by many of the later- 

 formed lamellse, which are laid down around the original beam as well as on the inner 

 side of the wall. Correris ('94) found that after successive treatments with concentrated 

 sulphuric acid and water numerous spheerocrystals were formed which were undoubtedly 



Fig. 150. Caulerpa crassifolia (Ag.) J. Ag. forma mexicana J. Ag. \ natural size. 



derived from the bulk of the membrane. These differed in several important respects 

 from similar sphserocrystals of cellulose obtained by Gilson and others, a,nd Correns 

 concluded that the cell- wall of Caulerpa did not consist of true cellulose but of ofte of the 

 allied substances. With iodine and sulphuric acid the wall colours only a golden yellow. 



The building-up and the strengthening of the walls and trabeculse of Caulerpa have 

 furnished much evidence in favour of the growth of cell-walls by apposition. 



The protoplasm is disposed as a parietal layer on the inner side of the 

 wall, and it also covers all the trabeculse, numerous anastomosing strands 

 passing from the thin layer around each of the trabeculse to the peripheral 

 parietal layer. Most of the strands run more or less longitudinally, and it is 

 not unlikely that one function of the trabeculse is to give support to this 

 delicate anastomosis of protoplasmic strands. In short, without this support 

 it would scarcely be possible for the delicate protoplasmic threads to ramify 

 through the large central vacuole of the coenocyte. Numerous nuclei are 

 present everywhere through the protoplasm, and there are also numerous 

 disc-shaped chloroplasts, mostly aggregated in the peripheral layer. The 



