436 



MOSSES AND FERNS 



CHAP. 



the young fertile segment of the leaf of Schi::cea, where the 

 relation of the sporangia to the leaf margin is very similar. 



Up to the time the cavities begin to form, the young fruit 

 is composed of uniform tissue, but shortly after, the tissue sys- 

 tems become differentiated, and the peduncle of the sporocarp 

 is formed. At this time the vascular bundle of the peduncle 

 can be recognised, and joins that of the sterile segment near 



B, 



SjC, 



Fig. 255. — Marsilia quadrifolia. A, Horizontal section of very young sporocarp, X500; 

 B, transverse section of an older sporocarp; ^ c, sorus canal; sp, young sporan- 

 gium, X about 340; C, horizontal section of young sorus showing the large apical 

 macrosporangium, and the lateral microsporangia, mi; in, the indusium. (After 

 Johnson.) 



its base. The peduncle is much longer in P. Americana than 

 in the very similar P. globulifera. The circinate coiling of 

 the sterile segment is repeated, though less conspicuously, here, 

 and the body of the sporocarp is bent at right angles to the 

 peduncle. 



