ORGANOGRAPHY. 
45 
latter of which are always called fronds, and are variously traversed 
by veins, ramifying in a determinate manner in the different genera. 
Upon certain definite parts of these veins, generally on the under 
side of the frond, termed the receptacles, clusters or lines of free 
one-celled spore-cases (sporangia) are produced, or occasionally 
many-celled ones ( synangia ), and in these cases the reproductive 
spores are contained. The clusters are called sori. 
VERNATION. 
The word vernation, as employed by me, designates the mode of 
growth of Ferns, or, in other words, the manner in which their 
fronds are developed and connected with the stem. 
Vernation is either — 
Articulated when the fronds are attached to the stem by a joint, 
and leave a clean scar when they fall away ; or, 
Adherent when no such joint exists, and the bases are continuous 
with the stem. 
And it is either — 
Uuiserial when the fronds are produced one after the other, in a 
single lineal series, sometimes close together (contiguous), 
and at other times far apart (distant) ; or, 
Fasciculate when they surround a central axis, upon the top of 
which they form a crown. 
STEM. 
In a large number of Ferns the stem is not at first sight very 
evident ; and even when plainly visible, it is frequently confounded 
with the root by the unlearned (as, for example, the underground 
stems of Pteris aquilina) ; but in others, as in Tree-ferns, it 
is very marked. It is an organ of considerable importance for 
classifying purposes, and often affords valuable distinctive cha- 
racters. 
The principal modifications of the stem are the — 
Pihizome, a brittle, fleshy, prostrate stem, producing roots along its 
under side, mostly growing above ground (epigeeous), and 
then furnished with scales (sguamose), but occasionally 
under ground (hypogceous), and then destitute of scales. It 
