PELAGIC PLANT LIFE 337 



This is true also of the attached algae, which develop upon 

 driftwood, vessels, and other large objects. They show that 

 germs of littoral organisms abound in the open sea, and are far 

 more numerous than our random samples would seem to 

 indicate. In May 1904, when cruising in the Norwegian Sea, 

 in lat. 67° N., where the bottlenose whales are annually shot, 

 we came across some wadding from a whaler's gun drifting in 

 the sea, the lower side of which was thickly overgrown with 

 attached forms of littoral diatoms. 



Castracane, after examining the first big collection of pelagic Geographical 

 diatoms from all the seas of the world made by the " Challenger " offhe^^gia'^c 

 Expedition, came to the conclusion that there was no essential aigje. 

 difference between the flora of the different areas. In this, 

 no doubt, he was right to a certain extent, since many species 

 are very widely distributed ; still a closer study has shown us 

 that there are definite marine areas and conditions of existence 

 in which they develop in vast numbers, whereas in other localities 

 they occur perhaps in such small quantities that only their 

 skeletons in the bottom-samples furnish evidence that they have 

 actually been present. Besides, we often find that species with 

 a wide distribution have different forms in the different areas, 

 though we have not yet the means of deciding whether these 

 forms diverge from the main type by virtue of hereditary 

 characteristics, or whether they merge into one another through 

 constant modifications. But in any case these forms are 

 characteristic of the flora of a given locality, and any one 

 who examines plankton-samples will become aware that it is 

 nearly always possible to determine the area from which they 

 have come. During the German Plankton Expedition under 

 Hensen in 1889, Schiitt convinced himself that the different Schutt. 

 currents had their characteristic flora, and he was at a loss 

 to understand how it is that local boundaries of distribution 

 can continue, seeing that the currents are ever carrying off the 

 microscopic plant-life from one part of the ocean to another, 

 and it might consequently be expected that all differences would 

 be obliterated. 



Schutt has also given a good description of the character of 

 the plant-life in different parts of the Atlantic, but the honour 

 of being the first to systematically investigate the distribution of 

 all the different species, and the influence exerted upon them 

 by ocean currents, must be assigned to the Swedish biologist cieve. 

 Cleve. A chemist by profession, he had for many years made a 



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