

16.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 71 



necessarily puts a term to the life of the organism. It is in these 

 plants that distinct sporangia are to be found. 



In the Algae and Fungi, the sporangium, when present, con- 

 sists of a single cell (or a ccenocyte). It may be comparatively 

 undifferentiated, as in Bangiaceae and other Florideae, where it is 

 simply a cell of the thallus the contents of which form one or 

 more spores ; or it may be a distinctly differentiated organ as 

 in the Cutleriaceae, Sphacelarieee, Ectocarpese, Laminarieae, and 

 some Florideae, among the Algae ; and in the Phycomycetes and 

 Ascomycetes among the Fungi. 



In all plants higher than the Algae and the Fungi, the sporan- 

 gium is multicellular. It is, however, unilocular, that is, it contains 

 but one cavity in which spores are developed, though this is some- 

 times chambered by incomplete walls (trdbecMlce) as in Isoetes. 



In the Muscineae, where the sporophyte apparently produces 

 only a single sporangium, termed the capsule or theca, this organ 

 constitutes the whole (Riccia) or a considerable portion of the 

 sporophyte. Its structure is simple in Riccia and other Hepaticae 

 but it becomes highly elaborate in the true Mosses (e.g. Polytri- 

 chum). It must, however, be borne in mind that the theca of the 

 Muscineae is not completely homologous with a single sporangium 

 of a Fern or a Phanerogam, but with at least a cluster (sorus) of 

 such sporangia : hence the exceptional complexity of its structure. 



In the Pteridophyta and the Phanerogams the sporophyte pro- 

 duces a number of sporangia. In the heterosporous forms there 

 are two kinds of sporangia which respectively produce the two 

 kinds of spores : those which produce macrospores are termed 

 macrosporangia ; those which produce microspores, microsporangia. 

 In the Phanerogams the macrosporangium is commonly termed 

 ovule, and the microsporangium pollen-sac. 



When the shoot of the sporophyte is differentiated into stem 

 and leaf, the sporangia are generally borne on the leaves (sporo- 

 phylls) : but in some plants they are borne on the stem. This 

 is the case in most Selaginellas, among the Pteridophyta : the 

 macrosporangia (ovules) are borne on the stem in various Phane- 

 rogams ; among Gymosperms, in the Taxeaa, and Gnetaceae ; among 

 Angiosperms, in the Polygonaceae, Chenopodiaceae, Amaranthaceae, 

 Primulaceae, Compositae, Gramineae, Naiadaceae, Piperaceae, and 

 others, the macrosporangia being either terminal or lateral : the 

 microsporangia are less commonly borne on the stem, but this is 

 the case in some Angiosperms, such as Naias and Casuarina. 



