678 HYDROPTERIDES. (mARSILIACE^E.) 



1. MARS ILIA, L. Maesilia. 



Submersed or emersed aquatic plants, with slender creeping rootstocks, send- 

 ing up elongated petioles, which bear at their apex a whorl of 4 nervose-veined 

 leaflets, and at or near their base, or sometimes on the rootstock, one or more 

 globular but somewhat eccentric sporocarps. These sporocarps or fruit are 2- 

 celled vertically, and with many transverse partitions, and split or burst into 2 

 lobes at maturity. On the partitions are inserted numerous short-stalked spo- 

 rangia, of two sorts intermixed ; the larger ones containing a single oval or ob- 

 long spore, the smaller containing many very minute spores. (Named for 

 Aloysius MarsU'i, an early Italian naturalist, — therefore to be written Marsilia, 

 not Marsilea.) 



1. M. quadrifdlia, L. Leaflets broadly obovate-euneate, glabrous ; spo- 

 rocarps usually 2 or 3 on a short peduncle from near the base of the petioles, 

 pedicelled, glabrous or somewhat hairy. — In water, the leaflets commonly float- 

 ing on the surface ; Bantam Lake, Litchfield, Connecticut, Dr. T. F. Allen. 

 The only known habitat in America. (Eu.) 



2. M. uncinata, Biaun., with hairy leaflets, and villous short-stalked or 

 sessile sporocarps, solitary at the base of each petiole, will doubtless be found 

 in the northwestern part of Wisconsin. It has been confounded with the very 

 similar M. vestita, Hook and Grev., of the Southwest. 



2 . A Z 6 L L A , Lam. Azolla. (PI. 20. ) 



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 antheridia ? peltately attached to 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 con- 

 taining a few globular spores. (Name said to come from a£co, to dry, and oXXco, 

 to kill, being destroyed by dryness.) 



1. A. Caroliniana, Willd. Leaves ovate-oblong, obtuse, spreading, red- 

 dish underneath, beset with a few bristles. — Still water, New York to Illinois 

 and southward. Plant forming little mats on the water, 6" -12" broad. 



Salvinia nAtans, L., said by Pursh to grow floating on the surface of small 

 lakes in Western New York, has not been found by any other person, and 

 probably does not occur in this country. It is therefore omitted. 



