560 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



strictly aquatic, and often grow in deep water, where they are 

 never uucovered in the driest seasons. In Phylloglossum 

 (Fig. 118) the fronds are subulate or cylindrical as in Isoetes, 

 but the rhizoma is reduced to a mere point, while the roots 

 are dilated into tubers like those of Botrychium or Rhizo- 

 glossum, and the fruit is borne in the axils of the bractes of a 

 pedunculate spike. If there was some doubt as to the 

 affinities of Isoetes, there is none here, as the plant is a 

 complete Lycopod except in foliage. It occurs in Australia, 

 New Zealand, and Tasmania, in peaty soil. 



640. Selaginella is distinguished by its fiat mosslike habit, 

 and the evident differentiation of the fruit, the sporangia 

 consisting of bi-trivalved sacs containing a few large spores, 

 the antheridia of subglobose sacs filled with orange or scarlet 

 minute bodies which ultimately produce the spermatozoids. 

 Both are sometimes contained in the same axil, but they are 

 sometimes separate. The leaves are usually of different sizes, 

 calling to mind such genera as Hypopterygium (Fig. 99, d) and 

 GyathophoruTTb (Fig. 109). The rhizoma is generally creeping, 

 but sometimes tall erect stems tower up, having feathery 

 branches or fronds clad with leaves. In Lycopodium the 

 fruit is not at first sight so evidently distinguishable into 

 male and female, though in essentials it accords exactly with 

 Selaginella. The plants, moreover, though frequently trail- 

 ing, are more or less cylindrical, and sometimes rise into a 

 thickish trunk. The leaves are often subulate, but they are 

 sometimes flat, as in Selaginella, or form rigid scales. The 

 habit, in fact, assumed by the numerous species is extremely 

 various. Tmesipteris is remarkable for its pendulous habit, 

 very broad leaves, and vertically bursting sporangia, which 

 spring from the axis of the stipitate didymous fertile pinnse. 

 The leaves or pinnee are sometimes acuminate, sometimes 

 truncate ; but both characters exist together frequently in the 

 same specimen. Psilotum has triquetrous stems, with trilo- 

 cular sporangia, thus departing from the normal character, as 

 also in the small ill-developed setiform leaves. The minute 

 bodies contained in them burst when placed in water, and emit 

 a cloud of microscopic particles. 



