COLOURj DISTRIBUTION, ETC. 17 



The Red Weeds are, as a rule, of delicate structure, 

 and grow in deep water, or in pools, or other sheltered 

 positions. Their colour is fugacious, and is frequently- 

 destroyed by exposure to the influence of light. The 

 effect produced on them by this means differs in degree 

 according to the extent and duration of the exposure. 

 Some fronds are only reduced a few shades paler than 

 their natural tint ; others are turned yellow or green ; 

 and others are thoroughly bleached ; but this extreme 

 is not usually reached except in the case of dead speci- 

 mens. 



It is a common error among inexperienced collectors 

 to believe that plants in this abnormal — I might almost 

 say diseased — state are generically or specifically different 

 from their bright-coloured, healthy brethren ; but this 

 is a delusion which a little practice will dispel. 



The class of Grass-green Weeds includes the remainder 

 of the Sea-weeds, and in addition a very large number of 

 fresh-water species. The marine portion, with which 

 alone I am at present concerned, grow in shallow pools, 

 and on the sides of rocks near the surface, but not 

 usually where they are altogether deprived of water by 

 the receding tide. Many species, notably some of the 

 EnteromorphiB, seem to grow indifferently in quite fresh 

 or quite salt, or any intermediate degree , of brackish 

 water, and nearly all the class love the light, and rather 

 gain than lose colour when exposed to the brightest rays 

 of the sun. There are, however, deep-water species 

 which boast as bright a green as their companions on 

 the shore, and it is therefore evident that light is not an 

 indispensable agent in the production of their colour. 



Several species of Olive and Red weeds are very beauti- 

 fully prismatic when in the water, as the light falls on 



c 



