Varietäten, Descendenz, Hybriden. — Physiologie. 517 



lui semblent etre favorables ä sa theorie, l'auteur la resume dans 

 les phrases suivantes: 



De nouvelles especes sont nees par un croisement entre especes 

 dejä existantes. L'espece nouvellement nee est prete et constante et 

 n'est soumise ä aucune forme de variabilite hereditaire ä la seule 

 exception possible, mais improbable, d'une perte accidentelle de 

 facteurs. 



La nature fait donc des sauts, mais ces sauts peuvent etre 

 excessivement petits. Ce n'est pas la grandeur du saut qui Importe, 

 ce qui est essentiel. c'est l'absence des formes de transition, dites 

 Varietes entre deux especes affines. 



La nature ne peut pas fabriquer d'especes par selection d'indi- 

 vidus, appartenant ä une espece donnee, parce qu'une teile selection 

 doit forcement rester sans effet par suite du fait que tous les indi- 

 vidus appartenant ä la meme espece ont une Constitution here- 

 ditaire identique. En un mot toute selection intraspecifique est 

 irapossible. 



La selection interspecifique reste possible, mais eile entre dans 

 le domaine d'une autre discipline, de celle qui concerne la survi- 

 vance entre especes dejä nees et sort donc des limites de cette 

 Conference, qui ne traite que de l'origine des especes. 



M. J. Sirks (Haarlem). 



Boysen- Jensen, P., Studier over Havbundens organiske 

 Stoffer. [Studies in the Organic Matters of the Sea-bottom]. 

 (Beretning XXII fra den danske Biologiske Station. Kobenhavn. 

 p. 1-36. 1914.) 



In an earlier paper the author suggested that the plants of the 

 Zosteya-he\t and not the plankton organisms were the main source 

 to the organic matter of the sea-bottom of many parts of the Danish 

 Seas. This hypothesis has been tried more thoroughly now, and the 

 present paper is the result of the investigation. 



Zostera is much richer — relatively — in pentosane Compounds 

 than the plankton organisms; the organic matter of the sea-bottom 

 was intermediate in this respect. A closer discussion of this subject 

 gave the result, that the organic matter of the sea-bottom of the 

 more land-locked waters (bays etc.) nearly exclusively was derived 

 from the Zostera; in the more open coast- waters (e. g. Kattegat) it 

 is probable that the plankton organisms play a not wholly inconsi- 

 derable röle as source of the organic matter of the sea-bottom. 



Calculations of the amounts of plankton and Zostera produced 

 per 1 m- in the Danish Seas inside the Skaw gave the result. that 

 the production of phytoplankton was ca. 100 gr. and that of Zostera 

 ca. 120 gr. pr. 1 m". It is supposed that only a small part of the 

 plankton production is deposited on the sea-bottom, and that this 

 Reposition occurs evenly on the bottom. The Zostera deposition on 

 the other band is mainly restricted to the more landlocked waters. 

 This result agrees in the main with that of the chemical analysis. 



The organic matter of the sea-bottom contains more nitrogen 

 than the Zostera; it was found that the later stages of decomposition 

 of the Zostera contained more nitrogen than the earlier stages. This 

 fact may be explained either by supposing that the nonnitrogenous 

 matter is destroj^'ed more quickl}^ than the nitrogenous, or by sup- 

 posing an assimilation of nitrogen , or by both processes combined. 



Through filtering sea-water from the Limfjord at Nykebing 



