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 thou<i;ht 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 libei'ated from their parent 



