606 HYDROPTERIDES. (MARSILEACE^E.) 



high and lo\* water mark, Dr. Zantzinger : and probably throughout the Middle 

 States. 



3. I. Engelm&lllli, Braun. Leaves long and slender (9' -12' long), 

 entirely emersed in summer, soft and flaccid, light yellowish-green, the dilated 

 base longer than broad ; spores coarsely farinaceous and reticulated. Shallow 

 ponds of the Western States, and southward. 



2. AZOLLA, Lam. AZOLLA. (Tab. 14.) 



Plant floating free, pinnately branched, clothed with minute imbricated leaves, 

 appearing like a small Jungermannia : fructification sessile on the under side of 

 the branches, of 2 sorts. Sporocarps covered at first with an indusium of a 

 single diaphanous membrane, ovoid ; the smaller kind opening transversely all 

 round, containing several roundish-angular antheridia ? peltately borne on the 

 sides of a central erect column : the large or fertile kind bursting irregularly, 

 filled with numerous spherical sporangia rising from the base on slender stalks, 

 each containing a few globular spores. (Name said to come from ao>, to dry, 

 and 6'XXo>, to kill, being destroyed by dry ness.) 



1. A. Cciroliiimfiici, "Willd. Leaves ovate-oblong, obtuse, spreading, 

 reddish underneath, beset with a few bristles. Pools and lakes, New York to 

 Illinois, and southward. Plant ' to 1' broad. Probably the same as A. 

 Magellanica of all South America. 



MARS^LEA MUCRONATA and perhaps M. VEST!TA may occur in the western 

 parts of Illinois and Wisconsin. 



SALVINIA NATANS, L., said by Pursh to grow floating on the surface of 

 small lakes in W. New York, has not been found by any other person, and prob- 

 ably Joes not occur in this country. It is therefore omitted. 



