INTRODUCTION. XVli 



various anomalous shapes that they assume are almost sure 

 to deceive a young botanist into the belief that the varieties 

 are so many different species. 



Many Algae, whilst growing under the surface of the 

 water, reflect colours which perish almost immediately after 

 they are removed to the air. Of this class are several spe- 

 cies of Cystoseira, especially C. ericoides, which, though 

 really of a greenish olive, appears, when growing under 

 water, to be clothed with the richest phosphoric greens 

 and blues, changing momently, as the branches move to 

 and fro in the water. Similar colours have been observed, 

 though in a less striking degree, on some species of the 

 red series. The genus Iridcea derives its name from this 

 character, though our /. edulis is not remarkable in this 

 respect. Miss Ball and Mr. W. Thompson have observed 

 Chondrus crispus to be occasionally iridescent. At the 

 Cape of Good Hope, Champia compressa and Chylocladia 

 capensis present very brilliant rainbow colours. Miss 

 Hutchins observed that Conferva Hutchinsics has change- 

 able glaucous tints when fresh, and looks almost white 

 when seen through the water. The cause of these brilliant 

 colours has not been particularly sought after. 



There are other species which really change colour 

 shortly after their removal from the water, as the various 

 kinds of Sporochnoideae, which pass rapidly from a clear 

 olive to a verdigris-green. But this is the effect of death 

 and incipient decomposition, for with the colour they lose 

 their crispness, become flaccid, and emit an offensive 

 odour, and, as has been observed by botanists, possess the 

 remarkable property of changing the colour of other small 

 filiform Algae with which they may come in contact. No 

 doubt this is owing to the development of some active 

 chemical agent. Professor Mertens, in describing the cir- 

 cumstance as occurring with Desmarestia ligulata and 



b 



