352 MARSILIACE^E. Pilularia. 



2. PILULARIA, Linn. 



Sporocarps globose, longitudinally 2 - 4-celled, dehiscent from the apex ; the cells 

 with parietal placenta-like cushions bearing in the upper portion microsporangia, 

 and below these numerous sporangia containing solitary macrospores. Plants with 

 a slender creeping rhizome and tiliforni leaves ; the sporocarps subsessile or peduncled 

 on the rhizome in the axils of the leaves. 



Five species are known. They grow in the muddy borders of ponds and in occasionally inun- 

 dated places in America, Europe, Northern Africa and Australia. 



1. P. Americana, Al. Braun. Leaves setiform, 1 inch long : sporocarps about 

 a line in diameter, attached by the side to a short descending peduncle, usually 

 3-celled ; macrospores in each cell 1 3 to 17, not constricted in the middle. Monatsb. 

 Acad. Berlin, 1863, 435, and 1872, 666. Pilularia, Nuttall, Fl. Arkans. 140. 



Near Santa Barbara (Mrs. Ellwood Cooper), May, 1879 ; Arkansas (Nuttall) ; also in Chili. 

 Less than half as large as the European P. globulifera, which has erect and regularly 4-celled 

 sporocarps. 



ORDER CXXV. SALVINIACE.S1. 



Floating plants with a more or less elongated and sometimes branching axis bear- 

 ing apparently distichous leaves : conceptacles very soft and thin-walled, two or 

 more on a common stalk, 1 -celled and having a central often branched receptacle 

 which bears either macrosporangia containing solitary macrospores, or microspo- 

 rangia containing numerous microspores. 



The order consists of two genera, Salvinia, not represented in the United States, and Azolla, 

 having each but very few species. The order is often united with the last, under the name of 

 Ehizocarpece.. 



1. AZOLLA, Lam. 



Small moss-like plants, the stems pinnately branched, covered with minute imbri- 

 cating 2-lobed leaves, anil emitting rootlets on the under side. Conceptacles in pairs 

 beneath the stem, either both containing macrospores, or one of each kind : smaller 

 conceptacles acorn-shaped, containing at the base a single macrospore, and in the 

 upper part several corpuscles of unknown character. Larger conceptacles globose, 

 having a basal placenta which produces many pedicelled sporangia containing sev- 

 eral masses of microspores. 



In a paper on Azolla Nilotica by Mettenius (in Plantse Tinneanse) is found one of the best 

 attempts to explain the curious fructification of this genus. Four species are described. 



1. A. Caroliniana, Willd. Plant 4 to 12 lines broad, much branched : leaves 

 with ovate lobes, inferior lobe reddish, superior one green with a reddish border : 

 corpuscles three to each macrosporangium ; macrospores with a minutely granulate 

 surface: masses of microspores glochidiate. Sp. PI. v. 541; Mettenius, Limnea, 

 xx. 278, t. 3, fig. 9-15, and PI. Tinneanse, 53; Gray, Manual, 5 ed. 606, t. 14. 

 A. microphylla, Kaulf. Enurn. 273. 



Floating, commonly on quiet waters, not rare. Oregon to Arizona, eastward to the Atlantic, 

 and southward to Brazil. An inconspicuous plant, looking like a purplish Hepatic moss. 

 A. Mayellanica is kept apart by Mettenius under the name of A. Jiliculoides, Lam. 



