310 
Class II. GYMNOSPERMS. 
Synorhiz^, Rich. Anal. duFr.Eng. ed. (1819). — Phanerogames Gymnospermes, Ad. 
Brongniart Veget. Foss. 88. (1828). — Gymnosperm.®, Nixus Plantarum, 21. (1833). 
Essential Character. — These agree in all respects with Exogens, except that their 
ovules instead of being enclosed in a pericarp are exposed naked to the fertilizing influ- 
ence of the pollen. 
The plants comprehended in this class have nearly an equal relation to 
flowering and flowerless plants. With the former they agree in habit, in the 
presence of sexes, and in their vascular tissue being complete ; with Ferns and 
Lycopodiums, among the latter, they also accord in habit, in the peculiar gy- 
rate vernation of the leaves of Cycadaceae, in their spiral vessels being imper- 
fectly formed, and in the sexes being less complete than in other flowering 
plants ; the females wanting a pericarpial covering, and receiving fertilization 
directly through the foramen of the o\mle, without the intervention of style or 
stigma, and the males consisting of leaves imperfectly contracted into an an- 
ther bearing a number of pollen- cases upon their surface. So great is the re- 
semblance between Lycopodiums and certain Coniferss, that I know of no ex- 
ternal character, except size, by which they can be distinguished. Gymnos- 
perms are known from most other Vasculares by the vessels of their wood 
having large apparent perforations or disks. It is not, however, on this 
account to be understood that these difier in growth from other Exogenous 
plants ; on the contrary, they are essentially the same, deviating in no respect 
from the plan upon which Exogenous plants increase, but having a kind of 
tissue peculiar to themselves. 
At this point of the vegetable kingdom there is a plain transition from the 
highest form of organization to the lowest. Gymnosperms are essentially 
Exogens in all that appertains to their organs of vegetation ; they have con- 
centric zones in their wood, a vascular system in which spiral vessels are found, 
and a central pith ; but they are analogous to reptiles in the animal kingdom, 
inasmuch as their ova are fertilized by direct contact with the pollen. The 
two most remarkable of the orders are Coniferse and Cycadaceae. Of these, 
the former is connected with Lycopodiaceae among Acrogens by means of the 
extinct genus Lepidodendron (see Fossil Flora, vol. 2. t. 98), and their 
branches are sometimes so similar to those of certain Lycopodiums themselves 
as to leave no doubt of their relation. Compare, for instance. Lycopodium 
Phlegmaria, and Cunninghamia sinensis. Cycadaceae have the gyrate verna- 
tion of the leaves of true Ferns, along with the inflorescence of Coniferae ; and 
their mode of forming their trunk, although essentially the same as that of 
Exogens, yet resembles in a remarkable degree the growth of Acrogens, 
lengthening by a terminal bud only. It is usual to refer Equisetaceae to Acro- 
gens, but I consider them a degenerate form of Gymnosperms for reasons that 
are explained under the order itself. 
