212 THE RED SEA COLOURED 



of an animal, when we come to investigate such minute 

 organisms as those we are now considering ; but it is, 

 at least, certain that mere motion, such as has been 

 observed in the Diatomacece, is no proof of animality. 

 And as the other points in their history ally them to 

 the vegetable kingdom, the fact of their vegetability, 

 if not quite proved (as I believe it to be), is, at least, 

 extremely probable. I cannot enter in this place into 

 the classification of these singular plants. The best 

 account of the British species is to be found in several 

 papers communicated by Mr. Ralfs to the Botanical 

 Society of Edinburgh, and published in the " Annals of 

 Natural History," in which figures of many species are 

 given. Figures of a few others have appeared in 

 " English Botany," and in " Grev. Crypt. Scot. ;" but 

 a general history of the group remains a desideratum, 

 which, it is to be hoped, Mr. Ralfs or Mr. Thwaites 

 perhaps the only persons in Britain capable of doing 

 full justice to the subject will favour us with. Both 

 genera and species are extremely numerous, and, no 

 doubt, great numbers await, in our waters, the eye of 

 the naturalist, ready to reward him for his pains with 

 a rich harvest of novelty and beauty. 



Before dismissing the subject of microscopic vege- 

 tables, I may remark that the colouring of the waters 

 of the Red Sea is now generally supposed to be caused 

 by the presence of countless multitudes of a minute 

 Alga, which is perfectly invisible to the naked eye, 

 except when great numbers are congregated together. 

 Some writers have denied that the water of the Red 

 Sea has any peculiar colour, or that its name is owing 



