468 Algae. 



H. H. Gran. This author has explained the origin of the 

 large diatom-masses in the following way: in the open sea 

 the supply of nourishment is very searce, while it principally 

 comes from the coasts or perhaps while the decomposition of 

 nitrogeneous matter is more intense in the warmer waters 

 of the open Atlantic Ocean; therefore the rapid evo- 

 lution of diatoms in large quantities can only occur in coast 

 waters and in boundaries of currents; and that the phenomenon 

 occurs in coast waters is caused by the fact, that so many of 

 the coast plankton diatoms produce resting spores. These 

 spores are left on the bottom in shallow water while they are 

 heavier than the normal cells; they rest there imtil the next 

 period of growing when they suddenly and rapidly develop and 

 multiply enormously. Against this theory Mr. Jörgensen 

 has several objections: If the theory were right, there 

 would be good reason to conclude that the masse-evolution 

 was a local phenomenon, each fiord having its special domi- 

 nant species and the time of the beginning of the development 

 being different m different fiords according to different local 

 conditions. But there is such a remarkably great uniformity 

 that it is difficult to think of the phenomenon as a local one; 

 furthermore it occurs simultaneously at different places. 



Another objection is that a large number of species forming 

 the bulk of the great masses do not occur otherwise in the fiords, 

 but are foreign forms, mostly arctic. Based upon these facts 

 and upon some other remarks Mr. J örgensen concludes, that 

 the predominating species of the masse-evolution in the spring 

 are brought in from the ocean by arctic water and under these 

 better conditions multiply suddenly and thus form the „inflow 

 of diatoms". With regard to the resting spores he thinks that 

 they are perhaps to be regarded as a reaction against plasmo- 

 lysis caused by salter water. — The author finds that the hydro- 

 graphers have given such descriptions of the circulation of the 

 currents in the Norwegian Sea, that it will be in favour of his 

 hypothesis. 



3. Thespeciesfound in planktonandtheir distri- 

 bution and remarks on the new or critical forms 

 (p. 90-114). 



In this part the author gives many very useful remarks 

 regarding the definition of the species. Of the very difficult genus 

 Coscinodlscus he publishes a key of the plankton forms, of 

 which C subbullens Jörg, is new. Critical remarks of the 

 Thalassiosirae are also interesting. A new genus, Podosira 

 Jörg., is based upon Podosira glacialis (Green) Cleve (= Lan- 

 deria glacialis Gran). The treatment of the genera Nitzschla, 

 Achnanthes, Navicula (incl. Stauioneis) and Pleurosigma con- 

 tains many new observations; new species are Stanroneis Grani 

 Jörg, and Pleurosigma tenerum Jörg, (according to the expla- 

 nation of PI. VI! identical with P. Stuxbergl Cleve). Among 

 the Perldlneae the author has worked out especially the genera 



