Isoetes has long been the subject of investigation and discussion, but Hofmeister (io), as a result of his investigations on Isoetes lacustris, gave us in I862 the first detailed account of the life history of the genus; and in most particulars his interpretations have stood as correct up to the present time. He called special attention to the similarities existing between Isoetes and the Lycopods, and pointed out some of the homologies existing between Isoetes and certain Spermatophytes, especially the Conifers. Later morphological studies on Isoetes have been made by Bruchmann (4), Belajeff (2), Kienitz-Gerloff (i i), Farmer (8), Campbell (5), Arnoldi (i), Goebel (9), Scott and Hill (T4), Smith (I5), Stokey (i6), West and Takeda (I7), and, in a limited way, by others. But accounts of detailed studies of the female gametophyte and the embryo sporophyte are pretty well limited to the work of Hofmeister (io), Kienitz-Gerloff (ii), Farmer (8), Campbell (5), and Arnoldi (i). Hlofmeister investigated I. lacustris, a species found in the British Isles and in North and Central Europe. This species, according to Pfeiffer (I3), has megaspores 500-700 microns in diameter. Kienitz-Gerloff also used I. lacustris in his study of the embryo. Campbell worked on I. echinosporca var. braunii (I. brauniii), whose megaspores measure from 420 to 580 microns in diameter. Farmer studied material of I. lacustris, but 'most of his account deals with the development of the organs of the mature sporophyte. Arnoldi made a study of the female gametophyte of I. mtalinvermiana. This form is limited in its distribution to Piedmont, in Italy, and has large megaspores ranging from 66o to 88o microns in diameter. Isoetes lithophila Pfeiffer, used in the present investigation, is apparently limited in its distribution to a sma'l area in Central Texas, and has very small megaspores ranging in size from 290 to 36o microns. The mature gametophyte of this species exhibits a striking abundance o-f rhizoids after the first leaf of the embryo has appeared, as well as a conspicuous protrusion of gametophytic tissue, which for a time encloses the first leaf of the embryo and later remains as a sheath about the base of the leaf until the gametophyte disintegrates. Observation of ftiese prominent features led to the present investigation, and as it progressed, several interesting morpho-