PLAN OP THE NATURAL SYSTEM. 3-15 



sibly into others, so that their limits cannot be accurately defined; and 

 no perfect system can be constituted until all the plants of the globe 

 are known. Moreover, many artificial means are avowedly used in 

 all natural systems to aid the student. 



720. The early natural systems were very imperfect, being founded 

 on comparatively vague views of structure and affinity. Such were 

 the systems of Magnolius and Adanson. The sketch of a natural sys- 

 tem by Linnaeus was very incomplete, and even that of the celebrated 

 Eay was imperfect. It was not until the knowledge of structural 

 botany had advanced, that the affinities of plants were ascertained, and 

 the relative importance of the different characters discovered. The 

 natural systems of the present day recognize a certain subordination of 

 characters, founded on the fact that some organs are of more impor- 

 tance to the life of plants than others. The relative values of these 

 characters are determined by the study of organization, and are not 

 fixed by arbitrary rules. The following table will illustrate this 

 subordination of character: 



721 SUBORDINATION IN VALUE OF THE OEGANS or THE SAME CLASS. 



Relative Values. Elementary. Nutritive. Reproductive. 



1. Cellular Tissue. 



("Vascular Tissue f Embryo or Spore. 



Q J a. Spiral Vessels. J a. Cotyledon. 



] b. Ducts ] b. Radicle. 



^Stomata I c. Plumule. 



[ fl. Stamens and 



I T> T r \ Pistil, 



a j Root, Stem, Leaf, I 9 v . 



Frond, Thallus.] 2 '^ 



L t. Theca. 



/'Perianth. 



4. < a. Corolla. 



I b. Calyx, 

 flnflorescence, 



' J Torus, Nectary, 



1 Bract, Invo- 

 L lucre. 



722. Thus, cellular tissue occupies the highest place, as being most 

 universally diffused, and capable of carrying on all the functions; next 

 comes vascular tissue. By the consideration of these, the two great 

 divisions of cellular and vascular plants are determined. There is 

 nothing in the nutritive and reproductive systems of the same value as 

 cellular tissue. The embryo and its parts are reckoned as occupying 

 the highest place in the nutritive system, and as corresponding in value 

 with the vascular among the elementary tissues. In the same way 

 the other values are determined. In examining organs, it is essential 



