260 
ORGANOGRAPHY. 
BOOK I. 
which it is to be inferred, that, although in these plants no 
new parts are added, except at the point of the trunk, yet 
that the parts after being formed do grow both in length and 
breadth. 
Below the scars of the leaves are often (always?) found 
elliptical or roundish perforations, filled with a powdery 
matter. These have no obvious analogy in other plants, 
unless they are to be compared to the perforations in the 
rhizoma of Nymphaea. 
It may be easily understood, that, taking such a structure 
as is now described for the type of Ferns, the name Acrogens 
(or point-growers) is well applied to them; and that all the 
modifications of structure which exist in the small species 
are mere reductions of developement, or adaptations of the 
same type to peculiar circumstances. 
Their petioles, or stipes {rachis, W. ; peridroma, Necker), 
consist of sinuous strata of indurated, very compact tissue, 
connected by cellular matter ; and the wood of those which 
have arborescent trunks is formed by the cohesion of the 
bases of such petioles round a hollow or solid cellular axis. 
The organs of reproduction are produced from the back or 
under side of the leaves. In Polypod iaceae, or what are more 
commonly called dorsiferous ferns, they originate, either upon 
the epidermis or from beneath it, in the form of spots, at the 
junctions, margins, or extremities of the veins. As they 
increase in growth they assume the appearance of small heaps 
of granules, which heaps are called sort. If examined beneath 
the microscope, these granules, commonly called sporangia^ 
thecce^ capsules, or conceptacles, are found to be little, brittle, 
compressed bags formed of cellular membrane, partially sur- 
rounded by a thickened longitudinal ring {gyrus, annulus, 
gyroma), which sometimes at the vertex loses itself in the 
cellularity of the membrane, and at the base tapers into a 
little stalk. The sporangia burst with elasticity by aid of their 
ring, and emit minute particles named spores or sporules, from 
which new plants are produced : as from seeds, in vegetables 
of a higher order. Interspersed with the sporangia are often 
intermixed articulated hairs; and, in those genera in which 
the sporangia originate beneath the epidermis, the sori, when 
