236 
HISTORY OF BRITISH FERNS. 
the base of the young vigorous leaves springing from the 
centre. 
The fructification is contained within a hollow at the 
dilated base of the leaves, and varies with the position it 
occupies. The spore-cases at the base of the outer leaves 
contain roundish spores, marked on the top by three 
elevated radiating ridges; these, which are externally 
opaque, whitish, and rough with minute prominent 
points, separate at the ridges into three triangular valves, 
exposing an interior subglobose semi-gelatinous substance. 
The spore-cases found at the base of the inner leaves, 
contain more numerous minute angular spores, of a pale- 
yellow colour. 
Two distinct-looking forms of the Quillwort have been 
observed, the one having thicker, shorter, and more spread¬ 
ing leaves than the other ; in the latter they are more 
slender and erect. These have been thought distinct 
varieties, or even distinct species, by some botanists, but 
are more probably mere changes of the plants brought 
about by external circumstances, such as a sudden rising 
of the water in which they grow, which may account for 
the taller and more slender growth; or the larger number 
of the spores, not becoming liberated from their parent 
