XXll INTRODUCTION. 



to have the segments of their fronds split into many 

 divisions : this is the case in the variety Soho- 

 lifera of Rhodymenia palmata, also in the varieties 

 of Chondrus crispus, and Gracilaria multipartita; 

 their fronds, when grown in similar situations, be- 

 come narrow, and differ greatly in appearance from 

 examples of the same species taken from shallow 

 water. An attentive observation of the disposition 

 and structure of the fruit is the surest means of as- 

 certaining the order and genus to which the plant 

 should be referred ] for upon the structure, &c., of 

 the fructification of the algae is based the classifica- 

 tion of these plants. In default of fruit, the stu- 

 dent must have recourse to the investigation of the 

 structure of the plant itself : usually, however, each 

 species has peculiar characters in its appearance and 

 habit which, after a little experience, will soon ena- 

 ble him to recognize it, and distinguish it from 

 others. And it has been observed of the algae that 

 they are more frequently separated fii'om their place 

 of growth, and cast ashore during the period of 

 their fructification, than at any other time — this in 



