24 HISTORY OF BRITISH FERNS. 
which lies downwards produces the root, and that part which 
lies upwards produces the rudimentary stem. The spores 
are very minute cells of various shapes, mostly roundish, 
and often beautifully ornamented with markings on the 
exterior. They consist merely of a small vesicle of cellular 
tissue, and as they grow, this vesicle becomes divided into 
others, which again multiply and enlarge, until they form 
a minute green leaf-like patch, roundish, but irregular in 
outline, and unilateral, forming a primordial scale, or 
germ-frond, technically called the prothallus, on the under 
side of which certain germ-cells are produced. One of these, 
it appears, at length becomes the axis of development, and 
produces a small leaf or frond, which is usually very differ- 
ent in aspect as well as size from the mature fronds, and 
is succeeded by others, which acquire by degrees the 
characteristic features peculiar to their species. 
In annual Ferns the mature character is soon attained, 
but in those of perennial habit, two or more years of 
growth is required before they reach maturity, and a much 
longer period is of course necessary to those which acquire 
tree-like stems. They, however, in most cases soon begin 
to assume something of their peculiar appearance, so that 
by the time three or four of these young fronds are pro- 
