CLASSIFICATION. 283 



but a single genus (as Platanaceae, the Plane-trees), while 

 others comprehend a hundred, or even a thousand, as 

 Umbelliferse, and CompositaB. 



Cohorts, etc. Again, the orders, by some one or few 

 traits which they possess in common, are marshaled into 

 Cohorts ; the cohorts into Classes, and the classes into 

 Provinces. 



Subkingdoms. Viewed as a whole, the Vegetable 

 Kingdom subsists in two grand divisions, called the Pheno- 

 gamia and Cryptogamia, as first shown by John Kay of 

 England, 1682. This division depends on the habitual pres- 

 ence or absence of visible flowers, and is confirmed by im- 

 portant differences of internal structure, and of seeds. (See 

 pp. 16, 27, 43.) 



Provinces. Each subkingdom is again divided into two 

 provinces. 1st. The province Exogens includes all such 

 flowering plants as have seeds with 2 or more cotyledons in 

 the embryo, wood growing by external layers, leaves net- 

 veined, and their flowers never (or very rarely) 3-parted. 

 2d. The province Endogens includes all flowering plants 

 which have seeds with one cotyledon only, wood growing by 

 internal accretions, leaves parallel-veined, and flowers habit- 

 ually 3-parted. 3d. The province Acrogens includes all 

 flowerless plants with stems growing in length, or at the 

 point (akros) only ; as Ferns and Mosses. 4th. The prov- 

 ince Thallogens, is composed of plants of the lowest orders, 

 growing indefinitely in shapeless expansions with no distinct 

 axis ; as Lichen's. 



Classes. The subdivisions of the provinces are called 

 Classes ; there are two of each. 1st. The Exogenous Angio- 

 sperms have flowers with stigmas, and seed-vessels inclosing 

 the seeds. 2d. The Exogenous Gymnosperms are naked- 

 seeded, having neither stigmas, nor pericarp ; as Pinus, 



