234 FOUNDERS OF OCEANOGRAPHY 



quire to be mentioned further on in the discussion. Amongst 

 the microscopic plants of the plankton there are a few Algae 

 and an immense number of Diatoms. 



Trichodesmium erythrceum is one of the " blue-green " 

 algae, which, however, is of a yellowish-brown colour 

 and occurs as bundles or clusters of short hair-like 

 filaments in enormous abundance on the surface of some of 

 the warmer seas, especially in the Indian Ocean and the Red 

 Sea (hence so named). It is most irregularly distributed, 

 and may occupy narrow tracts miles in length, or patches of 

 large area, and then be totally absent in equally large adjoin- 

 ing spaces. Our knowledge of this phenomenon dates back 

 to the times of Cook's voyages in southern seas when the 

 tracts of yellowish discoloured water were referred to (in the 

 journal of Sir Joseph Banks) by the sailors' name of " sea- 

 sawdust." This and other swarms were also noticed by 

 Charles Darwin in the South Atlantic during the voyage of 

 the " Beagle " in 1835. 



Coccospheres and Rhabdospheres are minute unicellular 

 algae having calcareous plates and spines, found in very 

 great abundance throughout the open oceans, and especially 

 abundant, according to Sir John Murray, in the tropics — 

 though often overlooked on account of their minute 

 size. 



Diatoms are found most abundantly near the coasts and in 

 colder waters such as the Southern Ocean and the North 

 Pacific. They vary greatly in size and shape (globes, drums; 

 spindles, ribbons, hairs, etc.), but are usually of a yeUowish- 

 brown colour and are enclosed in siHceous shells (the frustules) 

 which may be elaborately and delicately carved and pro- 

 longed into spines and other projections. A few of the more 

 notable forms are : — 



Chcetoceras — a genus containing many species, some of 

 which are amongst the most abundant Diatoms in the 

 Irish Sea in late spring and early summer, and sometimes 

 again in late autumn. As many as 160 millions have some- 



