4 P. T. CLEVE, PLANKTON-RESKARCHES. 



rearrangement of his data for 1900 I cannot at present find time. I must therefore defer 

 my reply on tlie details to a future opportunity. At present I cannot treat of anything 

 uiore than questions of a more general nature and 1 will therefore begin with what 

 might be called 



Gran's »Dauersporeii>)-liypotliesis. 



Mr. Gran bas from the beginning made the statement that diatoms which live along 

 the coasts, i. e. the neritic ones, produce resting sporcs, which dröp to the bottom and 

 remain there, imbedded in mud, until the circumstances for spiring become favourable. 

 Nobody has, as far as I know, hitherto hatched pelagic diatoms from spores buried in 

 the bottom-mud. Therefore Mr. Gran's statement is altogether hypothetical. It may be 

 possible that such small spores may fall down to the bottom in sheltered bays, but that 

 they, like heavy stones should sink down off the coasts, where the water is in continual 

 movement, from waves, currents and tides, seems to me inadmissible. The i-esting spores 

 are small (the largest of Cliotoceros-s^poreB only O, os to 0,o4 millim. in diameter), remain for 

 long time enclosed in the empty mother-cellules. They therefore may drift as well as the 

 vegetative chains to more or less distant regions. What becomes of them nobody knows, 

 therefore one hypothesis may be as good as another. The spines, simple or branched, 

 books, forks, bristles and hairs which in many cases cover the resting spores suggest the 

 idea to me that the spores may become fastened to drifting objects. We can perhaps 

 also imagine that they become swallowed by other organisms, and, as is the case with 

 several seeds, require this procedure for their spiring. Why these spores should neces- 

 sarily before spiring be buried in the bottom-mud is to me quite unintelligible. Consi- 

 dering the movements in the sea and the smallness of the objects the spores have pro- 

 bably to sink down to the »bJue mud», before they come to rest, a place scarcely favourable 

 for their spiring. The spore-formation is evidently a means for saving an organism when 

 the circumstances become unfavourable. The spores maj^ drift until they reach currents 

 with water favourable for the spiring. Pelagic copepods and others shed their eggs in 

 the open oceans. I imagine that there would not be any more difficulty for diatomspores 

 to develop in the sea than for pelagic eggs. 



It is true, as Mr. Gran has pointed out, that spores are formed chiefly by neritic, 

 not by true oceanic species. This may be explained by the frequent changes of the 

 qualities of the water, to which the neritic forms are exposed. We must not forget 

 that among the neritic species there is a large number, which never have been found 

 with resting spores. 



The next question I have to deal with is 



How far may plankton-organisms drift in the oceans? 



As bearing to some extent on this question and also on the question how far 

 resting spores can drift, I will first treat of the distances to which true litoral diatoms 



