INTRODUCTION. 33 



the name ot the genus. Go there, and among the 

 species you will find the plant in question. Suppose, 

 for example, that you have a frond of the Ptilota 

 elegans under observation, you will not find that in 

 the plates; but you will find a beautiful copy of a 

 Ptilota plumosa var. serrata, which you will see 

 much resembles your plant, but is not it. This will 

 lead you to the right genus, and then you wiU soon 

 have the thiug settled. 



Again, you will find " keys " at the head of all the 

 great divisions of the book, which if carefully used, 

 will lead you easily to the genus you are in search of, 

 and once there you will readily find the species sought. 

 Suppose, for example, you find a mass of curled and 

 kinky wool-like, green " Sea Moss," floating on 

 the tide or entangled with Alg» on the rocks ; looking 

 at it carefully tiU you observe that it is a simple un- 

 branched thread of green, you turn to the "key" for 

 Green Algae; the fi-ond is not membranaceous, so you 

 wiU not find it in the first group. It is fiHform, or 

 thread-like, therefore you will find it under one or the 

 other of the sub-division of this group. It is un- 

 branched, so you are sure to find it in the first 

 division, for there you read, "Frond unbranched, 

 sometimes attached straight and single, sometimes float- 

 ing, kinked and matted like wool," which is an account 



