77 



It was liowever in course of time discovered that each of 

 these groups contained plants as essentially different from 

 each other in physiological circumstances as the primary 

 groups themselves, and hence each has been subdivided, 

 and the number of classes increased to six, in the following 

 manner. 



1. In Exogens there are two totally different modes in 

 which the influence of the pollen is communicated to the seed. 

 The larger part of this primary group consists of plants pro- 

 vided with the apparatus called style and stigma, through 

 which the pollen-tubes are introduced into the ovary in the 

 act of fertilization. But others are so constructed that the 

 pollen falls immediately upon the seeds, without the intro- 

 duction of any intermediate apparatus; a peculiarity analogous 

 to what occurs among reptiles in the Animal Kingdom. And 

 as was to have been anticipated, the plants in which this sin- 

 gular habit occurs prove, upon being collected together, to 

 form a group having no direct affinity with those among which 

 they had been previously associated. Hence Exogens have 

 been broken up into 1. Angiosperms, or those having an 

 ovary, style, and stigma; and 2. Gymnosperms, which have 

 neither. 



2. Among Endogens, in like manner, two modes of propa- 

 gation have been discovered, essentially different from each 

 other. In the major part of them the result of the fertiliza- 

 tion of their seed is the production of an embryo, having one 

 point upon its surface predestined to become a stem, and 

 another to become a root ; besides which their elementary or- 

 ganization includes vascular tissue in abundance. But others, 

 although in a high state of developement, are wholly or nearly 

 destitute of vascular tissue, and where their seed is fertilized, 

 instead of an embryo being formed, the issue is a mass of 

 sporules, or reproductive bodies, analogous to those which 

 Acrogens have instead of seeds. The old class of Endogens 

 required therefore to be replaced by 3. SpermogeJis, whose 

 organs of propagation are seeds, and 4. Sporogens, commonly 

 called Rhizanths, whose reproductive bodies are spores. 



3. Among Acrogens also two modes of growth occur, so 

 essentially different from each other that they evidently repre- 

 sent difterent kinds of vegetation. In some of them there is 

 a distinct axis of growth, or stem and root, symmetrically 



