CHEMICAL SCIENCE. 201 



cess displaces another, previously preferred, but whose further devel- 

 opment is impeded by circumstances. 



THE COLORING MATTER OF THE RED SEA. 



To Ehrenberg is due the merit of having first described (in 1826) 

 the nature of the organism from which this coloring matter is derived. 

 He found it in the Bay of Tor, and called it Trichodesmium Erythra- 

 eum, which another writer, Montagne, advisedly changed to T. Ehren- 

 bergii. <l No one," says Mr. Carter, " who has read the memoir of 

 M. Danste on this subject, can doubt that this is not the only organism 

 which colors the sea red in different parts of the world." In June, 

 1862, Mr. Carter himself had an opportunity of seeing the color of the 

 Red Sea, on which he gives a few observations. When approaching 

 Aden, on May 31, he passed through large areas of a yellowish-brown 

 oily-looking scum on the surface of the sea ; and on June 2, when off 

 the Arabian side of the first island sighted in the lower part of the Red 

 Sea, after leaving Aden, it again appeared, and he frequently passed 

 through large areas of it. Only once, he saw a portion of brilliant red 

 and one of intense green together in the midst of the yellow. The 

 odor which came from this scum was like that of putrid chlorophyll or 

 like that from water in which green vegetables have been boiled. He 

 drew up some of this scum, and found it to be composed of little short- 

 cut bundles of filaments, like oscillatona. On examining the specimens, 

 microscopically, in January, 1863, he found the little bundles, which 

 were still just visible to the naked eye, like so much sawdust. Their 

 color was still faint yellowish to the naked eye ; but the filaments un- 

 der the microscope were faintly green. After referring to the evidence 

 of other observers, Mr. Carter considers that the occurrence of Trich- 

 odesmuim Ehrenbergii in the Red Sea, in the Gulf of Aden, the In- 

 dian Ocean and the Sea of Onan is so far substantiated ; and as the 

 yellow color, in all instances, probably passes into red, we have appar- 

 ently the explanation of the whole of these seas having been called by 

 the Greeks, Erythraean (red). Next to the yellow color, red is most 

 prevalent and green least of all. Although Mr. Carter adds many 

 other interesting particulars, he concludes by saying that much yet re- 

 mains to complete the history of this little plant, which unfortunately, 

 can only be obtained by watching it long and narrowly in its habitat. 

 Annals of Natural History. 



THE NUTRITION OF PLANTS. 



One of the vexed questions in vegetable nutrition has long turned 

 upon the source from which plants derive their nitrogen. As this gas 

 is so abundant in atmospheric air, the early speculators naturally as- 

 sumed that plants derived their nitrogen from the air, by the simple 

 process of direct absorption. This was, however, subsequently shown 

 to be eminently improbable, and the very chemists who propounded 

 the hypothesis, retracted it. The denial has for many years been 

 stereotyped in text-books, and M. Dumas felt some hesitation in bring- 

 ing forward the recent discovery of a young chemist, M. Jobin, which 

 proves that the Confervas if no other plants really are capable of 

 the direct absorption of nitrogen, instead of receiving it by a decom- 

 position of nitrates. His experiments consist in placing Confervas 



