510 



HUTCHINSON'S POPULAR BOTANY 



Phanerogams, to which are attached megasporanges containing one large 

 spore, and microsporanges containing a large number of small spores. 

 The sporanges attached to each placenta constitute a sorus. The mega- 

 sporanges are chiefly the lower bodies of the sorus, and although at an 

 early stage of development the contents of each becomes broken up into 

 sixty-four cells, only one of these becomes mature and develops into a 

 megaspore. Each microsporange, however, produces sixty-four micro- 

 spores. The megaspore becomes invested, first, in a hard brown coat, 

 but later this receives an outer gelatinous coat the epispore consisting 

 of three layers, except at the apex of the spore where the two outer 

 layers are wanting, and the apex in consequence lies in a cavity whose 

 walls are the two outer layers of the epispore. At the apex the protoplasm 



breaks up into several cells, which 

 are not at first invested by cellulose, 

 but finally form a tissue containing 

 a little chlorophyll and developing 

 into a prothallium. The growth of 

 the latter causes it to break through 

 the apical layers of the megaspore 

 and project as a spherical body into 

 the cavity previously referred to. 

 In the centre of the prothallium 

 there is a large cell (afterwards the 

 archegone) covered by four other 

 cells, from which arise the neck and 

 stigmatic cells of the archegone. The 

 greater portion of the protoplasm of 

 the archegone contracts into an 

 oosphere (fig. 643). 



Each microspore divides into three 

 cells, of which one becomes a sterile 

 prothallium, but each of the other 

 two divides into sixteen cells, and the nucleus of each of these becomes 

 an antherozoida rod-like body coiled four or five times, to which are 

 attached a few cilia, by whose vibration the body is impelled. The anthero- 

 zoids find their way to the funnel above the apex of the megaspore, and 

 getting entrance by the neck of the archegone, reach the oosphere and 

 fertilize it. The result of this fertilization is the development of the 

 oosphere into an oosperm, which becomes invested with cellulose and 

 undergoes segmentation to form the embryo with its root, stem, first 

 leaf, and an attachment (foot) to the prothallium. Thus arises the 

 sporophyte like that by which the sporocarps were produced. The " leaves " 

 of Pilularia consist only of the petiole, no lamina being developed. In 

 the early stages these leaves are coiled up from the apex to the base, 



FIG. 651. PILLWORT (Pilularia globulifera). 



A diagrammatic section of one of the sporocarps, showinR 



clusters of megasporanges and microsporanges in each of 



the four compartments. 





