Peck u. Harrington, Plankton des Puget-Sound. 521 



uishes ground for estimates, bused upon actual counts; but we do 

 believe that it gives a true picture of the vertical distribution of cer- 

 tain forms at the time the samples were taken. 



In notes taken in connection with the collections upon which this 

 paper is based Harrington says: ,,Tow taken in Port Townsend 

 Harbor varied greatly on successive evenings. It was noticed after 

 a rain that the surface water had a muddled appearance, and that 

 the net was quickly clogged with a brown coating of Coscinodiscus 

 and Arachnodiscus while on other evenings comparatively few of these 

 were to be seen. The number of medusae varied very noticeably 

 with the roughness of the sea, falling of rain etc., and a strong 

 inshore wind always brought in various organisms such as masses of 

 Noctiluca u . He also states that the collection from which the plotting 

 was made was taken at the close of a week in which there had been 

 hardly any rain, and that in a glass jar the water was very trans- 

 parent, while a few copepods could be seen in some of the samples. 



The causes for the sudden appearance of a given pelagic organism 

 and its similar disappearance, in great numbers, are very obscure 

 although the facts have often been observed. Whipple 1 ), from ob- 

 servations in the several basins of the water supply of the city of 

 Boston, Mass., has attempted to throw light upon the seasonal increase 

 in certain diatoms by assigning as causes the vertical stirring up of 

 the water, and the necessary presence of Oxygen in connection with 

 the assimilation of nitrates by the growing cells. Many interesting- 

 data have thus been brought together by him, concerning the seasonal 

 growth of this organism in shallow fresh waters, but such conditions 

 would with difficulty be applied to marine forms over the much greater 

 depths here described, and it is probably true that there is more 

 fluctuation in shallow water and at the surface than in the deeper 

 strata. We also gather from the work of Prof. Joh. Walther 2 ) 

 summarizing the work relating to the depth to which light penetrates, 

 and its various spectrum absorption etc., that the bottom depths reached 

 by our analysis in Puget Sound are only about half the distance to 

 which the suns rays can penetrate under favorable conditions, and 

 also that the vertical sounded by us traverses a variety of colors in 

 the water that are due to the absorption of the several elements of 

 the light. 



It may be said in general, therefore, of the vertical distribution 

 here recounted, that the surface strata present the greatest numbers 

 of living individuals and furnish the most favorable, although irregular, 

 conditions for the growth and reproduction of these organisms; but in 



1) Some Observations on the Growth of Diatoms in Surface Water, Techno- 

 logy Quarterly, Vol. VII, Nr. 3, 1894. 



2) Bionoinie des Meeres, Jena 1893, p. 35. 



