40 ELEMENTS OB' BOTANY. 



entcrerl into in dctiiil lioro, for however nctivo cryptogamous plants may 

 be in the causation of diseaso — and Hurcly tliis is a vexed qucstioii just 

 now — they are not, as a rule, particularly eiiicacious in its cure, at least 

 so far as our present knowledge goes. 



Of the lowest orders we shall say nothing save that their life history is 

 similar to that of the lowest orders of the animal kingdom, being, in fact, 

 nothing but the history of single cells. 



The highest orders, termed acrogenous cryptogams, have a dis- 

 tinct axis, growing from its apex only, containing woody tissue and vessels, 

 and usually with some foliage. They are destitute of true flowers, but i)ro- 

 duce, instead of seeds, minute bodies termed spores. From these spores 

 are produced new plants, but in a manner altogether diflerent from the 

 germination of the seed of a flowering plant. In the first place, from the 

 spores are developed oi'gans analogous to stamens and pistils ; the latter 

 being fertilized by the former, a new plantlet is the result. In other 

 words, reproduction is not finally accomplished by the parent plant, 

 though the materials for its accomplishment are fully prepared. 



To this class Ijelong very few medicinal species, male fern {Af<pidii(m 

 Filix-ma>^), shield fern {A^indium marginalc), and club-moss [Lycopodiam) 

 being the only ones indigenous to North America. 



CLASSIFICATION OF PLANTS. 



Tlio unit of classification in vegetable as in animal life is the species ; 

 and a knowledge of all known species would, in one sense, comprise the 

 knowledge of the whole vegetable kingdom. But as species indicates a 

 rclationshij:) of individuals, so different sjiecies bear relationship to each 

 other, and groups of sj^ecies relationshiiis to other groups, and so on until 

 the entire vegetable kingdom is included. 



An illustration will best serve to define a species. Take, for example, 

 2:>eppennint. We have here a plaiit of a certain aspect, with stem, leaves, 

 flowers, and fruit to a certain extent peculiar to itself. The seed of one 

 individual or of a thousand will produce plants of essentially the same 

 character, year after yeai*, generation after generation. We might plant 

 beside this another of somewhat similar aspect, sj)earmint, and this would 

 also reproduce itself generation after generation without change. There 

 would never be an intermingling of the two ; the seed of the one would 

 never produce the other, but each would always reproduce itself. Now, 

 then, all the individual jieppei'mint plants existing are the direct descend- 

 ants of others which preceded them, and those of others still, and we can 

 reasonably trace the chain backward to one common ancestor. The sania 

 with spearmint. To express this history of a plant we use the term 

 species, signifying all individuals descended from a common stock. 

 Hence the species peppermint comprises all the individuals having its pe- 



