CHAPTER XVIII 



THE PRINCIPAL GROUPS INTO WHICH PLANTS NAT- 

 URALLY FALL, WHETHER BY RELATIONSHIP OR 

 HABIT 



Classification 



NE does not go far with the study of plants before he 

 perceives that they fall into groups, and groups within 

 groups, according to the degrees of their likenesses and 

 differences. Some kinds are so closely alike that 

 botanical experts dispute as to whether they really are different 

 or merely two forms of the same, while others are so very unlike 

 that they offer not the least point of resemblance; and there is 

 every gradation between. The arrangements of plants in their 

 groups, and of these in relation to one another, is Classification, 

 which we must now proceed to consider in so far as it has connec- 

 tion with the particular theme of this book. And we naturally 

 begin with the groups which are largest and best defined, of which 

 there are five, Algae, Fungi, Moss-Plants, Fern-Plants, and 

 Seed-Plants. 



The Algae. These are the distinctive plants of the waters, 

 comprising especially the Seaweeds, but also many kinds that 

 dwell in rivers and lakes, and a few that live out in the air. In 

 size they range widely, from kinds too small for the eye to detect 

 up to the great Macrocystis of the Pacific, whose thousand feet 

 (pretty nearly) of length surpasses anything that land plants can 

 offer. In shape they are bewilderingly multifarious, spheres, 

 cylinders, hairs, plates, tufts, fronds, and even leafy stems, which 



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