INTRODUCTION. XXI 



near low water-mark^ it is of a fine deep purple- 

 red y a little higher up it is a dull purple-brown ; 

 higher still a pale brownish-red, and at last, near 

 hig-h water-mark, it is often yellowish or greenish. 

 Chondrus crispus, too, when found in shallow water, 

 is often of a bright herbaceous greeny and Cera- 

 mium rubrum passes through every shade of red 

 and yellow, and at last degenerates into a dirty 

 white before it ceases to grow. All these species 

 vary in form and size as they do in colour, and the 

 various anomalous shapes that they assume are 

 almost sure to deceive a young botanist into the 

 belief that the varieties are so many different spe- 

 cies." The Cystoseira ericoides, when seen growing 

 under water, appears clothed in the most beautiful 

 rainbow hues, but when removed from thence is 

 found to be of a dark olive- green colour. A few 

 others possess this remarkable property, which is 

 termed iridescent. Forfn in the generality of the 

 flat-fronded algse is a character of little value ; 

 plants of the same species differ at times widely in 

 this respect. Deep-water specimens will be found 



