MA 
17 
It was however 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. 
_L In £zogens 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 ofany 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. Spermogens, 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 different kinds of vegetation. In some of them there is 
a distinct axis of growth, or stem and root, symmetrically 
