234 THE AMPHIBIOUS QUILLWORTS. 



rosette ; but in ri\ers w here the species are exposed to 

 more or less current the leaves are likely to be longer, 

 and, though arranged in circles, the rosette appearance 

 is often obscured because the flaccid leaves all extend in 

 the direction taken by the current. In the present 

 species the leaves are sometimes up- 

 ward of a hundred in number and 

 twenty or more inches long. Ordinary 

 forms, however, are usually less than a 

 foot in length. Being exposed to 

 the air for a large part of the year, the 

 Megaspore of Icavcs have abundant stomata, and 



Isoties Engehiiantii . 



the peripheral bast bundles necessary 

 to give strength to the aerial leaves are also present. 



The plants usually grow on the margins of streams. 

 During winter and spring they are covered by the 

 water, but as the waters diminish with the warm 

 weather the leaves are soon exposed to the air, either 

 by floating on the surface of tlie shallow water or by 

 being left entirely exposed. The leaves found early in 

 spring are the ones that bear the sporangia. They are 

 long and flaccid, and upon exposure to the air are likely 

 to decay, being replaced by circles of shorter recurved 

 leaves, some of which, if the season is long enough, may 

 also perfect sporangia. It is probable that these leaves 

 are normally sterile and alternate with the fertile leaves. 



The sporangia are unspotted and have a narrow in- 

 dusium. The spores are released by the decay of the 

 sporangium, and for some time after the leaves have 

 fallen the sporangia may be found attached to the plant. 

 The megaspores are from 350," to SSO/' delicately honey- 

 comb reticulated. Th-e microspores are 24/* to 28^" in 

 length, and nearly smooth. In the southern parts of this 



