220 THE AQUATIC QUILLWORTS. 



feet below the surface, a colony of plants like small 

 green rosettes, he may conclude that he has found 

 Braun's quill wort (Isoctes ecJiinospora Braunii). Since all 

 the aquatic quillworts have the same general plan for the 

 plant body, it is possible that such a conclusion may have 

 to be modified later and his specimens referred to some 

 other species, but Braun's quillwort is so abundant and 

 so widely distributed that until its spores have been ex- 

 amined one is fairly safe in assuming that any new find 

 is this species. 



The leaves are from ten to thirty in number and occa- 

 sionally reach a length of ten inches, though the average 

 is probably less than five. They are dark green, occasion- 

 ally reddish at base, and while in the water are half erect. 

 When fresh from the water they are somewhat rigid and 

 inclined to curve backward. There are a few stomata 

 present on the tips of the leaves, but the peripheral bast 

 bundles are absent, as is usual in the submerged species. 

 The sporangium is pale spotted, and the velum or in- 

 dusium about half covers it. 



The principal distinguishing charac- 

 ter is found in, the megaspores. These 

 are from 350^ to 550^ in diameter and 

 covered with broad spinules which are 

 often forked or toothed and sometimes 

 recurved. Occasionally, too, the spin- 

 ules may become confluent into short 

 crests. The microspores are from 26 v 



Isoetes ech inospora 



f- o OQ /j, in length, white or grey in 

 colour, smooth, and very numerous. Three hundred 

 thousand microspores have been found in a single 

 sporangium. The spores retain their vitality for some 

 time, and plants have been raised from the spores taken 

 from herbarium specimens. 



