52 



CHA.NGE OF TINT. 



branches. These details are of very minute size, 

 and cannot be made out without the assistance of 

 a magnifying glass. 



These dark-spored vegetables are very variable 

 in colour, as indeed are all the algse, without 

 reference to the colour of their spores; some- 

 times, indeed, even trespassing on the colour of 

 another sub-class. These changes are mostly due 

 to the varying depths of the sea where the plants 

 grow, and to the amount of light and shade 

 which falls to their lot. Even the hardy, rough, 

 and coarse bladder-wrack, which is usually of a 

 very dark olive-green, more approaching to black 

 than to green, becomes of a rich yellow tint when 

 found at any depth of water. 



When dried the green vanishes totally, the 

 colour changing to dark-brown, and in many 

 cases to black. Most of this sub-class of algse 

 require alternations of water and air, the best 

 specimens being found where they are exposed 

 to the heat of the sun and to the force of the 

 winds for some hours daily. 



