316 Mr C. G. Elircnbcre'^ii Observations on the 



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sure, accurately examined the appearance, and made microsco- 

 pical observations on tlie colouring mass. The flakes consisted of 

 small spiral, or longish irregular bunches oi oscillator iae ihreadsj 

 which were enclosed in a gelatinous sheath, and the flakes nei- 

 ther resembled one another nor the threads in each flake. JJK 

 the glasses placed beside me, I observed that the flakes, during 

 the heat of the day and in sunshine, flloated together on the"^ 

 surface of the Avatcr. During the night, and when the glasses 

 wdt^ shaken, they descended to the bottom. After some time 

 they returned to the surface. The observation made by Dlr 

 Engelliardt on Lake Murten, was very similar to this appear-' 

 ance, and the delineation of the single threads by De Candolle, 

 exhibits a very close relation to it. De Candolle informs 

 me he has preserved no dried specimen of that substance, for 

 which reason no comparison can be made. The gelatinous 

 covering, and the union of many threads into very small spirial 

 ffroups, ffivc to the substance of the Red Sea a peculiar eliarac^ 

 ter, which entitles it to lorm a particular genus or alga- ■. 



Trichodesmium erythreum. Char. gen. Fila septata fas- , 

 cicidata nee oscillantia, fasciculi dlscreti muco involuti socialei 



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lihere natantes. I know a very similar green body, which I have 

 often observed at Leipsic and Berlin, and which entirely fills 



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the water, giving it a greenish hue. I call it Triclhodesmium 

 Jlos aqua, because I do not find it enumerated among tJre 

 commonly mentioned forms of this kind, ' ^ "^^ ""^ '^^' 



The appearance of the Red Sea was not permanent out pe^^ ' 

 riodical. I observed it four times, viz. on the ^5th and SOtli'^ 

 December 1823, and cai the 5th January 1824. Webroughr'^ 

 along with us for the Royal Collections specimens taken froM „ 

 the sea shore, and dried on paper and sand. More pai-ticulaif^* " 

 details in regard to it will be found in the Symholi Phi^sici oi^^ 

 Dr Hem prich's journey and my own. ; . ' '] *:''■''"' ''i'^' yvy^ 



In 1829, I had an opportunity in Sifema SfStM^gmymc^^^^ 

 recent observations on blood-red waters. In the steppe of Plat^^" 

 taw,' between Barnaul and the lake of Koliwan, on the 24tli'^ ' 

 July (5th August, O. S.), while intending to take a survey ot ^- 

 the vegetation of the steppe, I found a fen with a pool ot 

 watei^j in a low land in the immediate vicinity oi" the post- 

 statiori. The dark blood-red colour of the water was very strike 



