134 



DEPTHS OF THE OCEAN 



cover the surface in one unbroken layer, a phenomenon which 



CErsted. CErsted observed in 1849, and which led him even then to 



look upon microscopic plants as the basis of production in the 

 sea. Besides the species of TricJiodesmi2Lm we have another 



Katapiymcne. gcuus, Katagjty 7716116, with Spiral series of cells in sheaths of 

 slime. Mention must also be made of 



Riciieiia. the remarkable little alga, Richelia 

 iiiti^acellulai'is, described by Jobs. 



Schmidt. Schmidt, which lives in cells belonging 

 to various species of Rhizosole7iia (see 

 Fig. 241). These diatoms appear to 

 have no difficulty in accommodating 

 their guest, which apparently repro- 

 duces itself within the cell, and is thus 

 transferred to new generations of the 

 hospitable plant. The riddle is, how 

 did it originally manage to get in ? 

 Most likely this happened at a stage 

 when the Rhizosoleiiia had not yet 

 developed the silicated cell-wall of the 

 hermetically sealed chamber with which 

 we are acquainted. 



The green colour which predomin- 

 ates in plants on land is practically 

 only to be found at sea in the globular 



Haiospiuzra. HalospIicE7'a vi7'idis (see Fig. 241). 



Schmitz. This has been described by Schmitz 

 from Naples, where the people call it 

 " punti verdi," that is to say, green 

 spots. It is or may be lighter than 

 sea-water, so that it floats quite close 

 to the surface. On the other hand, 

 Hensen's expedition found it at pro- 

 found depths, even at 1000 metres, 

 away down near the limit of the pene- 

 tration of sunlight, but if this denotes anything in its life- 

 history, it must be at any rate in a state of resting. HalospJi(E7'a 

 is reproduced by zoospores, though we do not know how they 

 proceed to form the small globular cells that little by little 

 grow up to the normal size. The cell-wall is so firm and 

 thick that its outer part is burst at last in the course of 

 growth and discarded, and the inner elastic parts are thus 



cieve. enabled to expand. Cleve has also observed thick -walled 



Y\G. 241. — Chains of Richelia 



INTRACELLULARIS WITHIN THE 

 CELLS OF RHIZOSOLENIA STVLI- 



FORMIS. (Karsten.) 



