I.ESSON 28.] CLASSIFICATION. 175 



vator's skilful care. If left alone, they are likely to dwindle and 

 perish, or else revert to the original form of the species. 



603. Botanists variously estimate the number of known species 

 of plants at from seventy to one hundred thousand. About 3,850 

 species of the higher classes grow wild in the United States east of 

 the Mississippi. So that the vegetable kingdom exhibits a very 

 great diversity. Between our largest and highest-organized trees, 

 such as a Magnolia or an Oak, and the simplest of plants, reduced 

 to a single cell or sphere, much too minute to be visible to the 

 naked eye, how wide the difference ! Yet the extremes are con- 

 nected by intermediate grades of every sort, so as to leave no wide 

 gap at any place ; and not only so, but every grade, from the most 

 complex to the most simple, is exhibited under a wide and most 

 beautiful diversity of forms, all based upon the one plan of vegeta- 

 tion which we have been studying, and so connected and so an- 

 swering to each other throughout as to convince the thoughtful 

 botanist that all are parts of one system, works of one hand, realiza- 

 tions in nature of the conception of One Mind. We perceive this, 

 also, by the way in which the species are grouped into 



504. Kinds. If the species, when arranged according to their re- 

 semblances, were found to differ from one another about equally, — 

 that is, if No. 1 differed from No. 2 just as much as No. 2 did from 

 No. 3, and No. 4 from No. 5, and so on throughout, — then, with all 

 the diversity in the vegetable kingdom there is now, there would yet 

 be no foundation in nature for grouping species into kinds. Species 

 .and kinds would mean just the same thing. We should classify them, 

 no doubt, for convenience, but our classification would be arbitrary. 

 The fadt is, however, that species resemble each other in very un- 

 equal degrees. Some species are almost exactly alike in their whole 

 structure, and differ only in the shape or proportion of their parts ; 

 these, we say, belong to one Genus. Some, again, show a more gen- 

 eral resemblance, and are found to have their flowers and seeds con- 

 structed on the same particular plan, but with important differences 

 in the details ; these belong to the same Order or Family. Then, 

 taking a wider survey, we perceive that they all group themselves 

 under a few general types (or patterns), distinguishable at once by 

 their flowers, by tiieir seeds or embryos, by the character of the 

 seedling plant, by the structure of their stemo and leaves, and by 

 their general appearance : these great groups we call Classes. 

 Finally, we distinguish the whole into two great types or grades; 



