78 DiATOirs. 



A few words here may be of interest concerning our 

 local flora. The Hudson River at Poughkeepsie is a 

 very good place for collections and no better place can 

 be found for this purpose than the filter-beds at the 

 pumping works. They furnish an ideal habitat. They 

 are cleaned at frequent intervals ; the water in them is 

 free from currents and is exposed constantly to the rays 

 of the sun, so that the diatoms collect in vast numbers 

 and as the water is lowered they sink gently to the bot- 

 tom and are deposited on the surface of the mud which 

 is held back by the layer of filtering sand. When the 

 water is all drawn off, by gently scraping the surface of 

 this mud myriads of diatoms can be obtained. A singu- 

 lar fact is to be noticed. During the summer months, in 

 July especially, the most frequent, or at least most con- 

 spicuous species, is a marine one. It occurs in the river 

 at this point and is much more frequent here than it is 

 further down the river. I failed to find it at all at Sing 

 Sing, although most of the forms there are marine. It 

 is called coscinodiscus subtilis and is a beautiful little 

 disc with fine radial markings arranged in groups or 

 bundles. In July, 1888, I got from the filter bed a 

 gathering almost pure of this beautiful little species. It 

 seems to have colonized here in the filter bed, and find- 

 ing suitable conditions for its grovrth has made a perma- 

 nent home. It grows the year round and I have collected 

 it every month in the year, but it is most abundant in hot 

 weather. The photograph of it is taken from a very 

 large specimen. In Florida this diatom grows to per- 

 haps twice the diameter of the largest here, and I 

 have specimens from the Richmond earth four times as 

 large, but these are exactly the same in markings and 

 are identical with our form. Other marine forms are 

 found here also in considerable variety, but no great 

 number of individuals. The marine forms are here evi- 

 dently as the result of back-water from storms at sea or 



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