ESSENTIAL ORGANS — THE OVULE. 



251 



ing the spores, and surrounded by a cellular coat resembling a calyx, c. 

 From this ovary-like body there is a prolongation which may be con- 



Fig. 446. 



Fig. 447. 



Fig 448. 



Fig. 449. 



sidered as a style, t, terminated by a cellular enlargement, s, which 

 has been compared to a stigma. The styloid pro- j 2 



longation withers and disappears when the spores 

 are mature. Sometimes the thecse, as in Lichens, 

 consist of a club-shaped elongated cell or ascus 

 (fig. 449, 1), coataining nuclei or cells in its in- 

 terior, which form the spores. Sometimes these 

 are single, at other times united in sets of two 

 (fig. 449, 2), or of four (fig. 447, 2), or of some 

 multiple of four. There are various modifications 

 of sporangia in other Cr3rptogamic tribes. In 

 Ferns, they are often surrounded by an annular 

 ring, or by elastic bands, which cause their de- 

 hiscence ; while in Ohara they are called nucules, 

 and present an oval form with a spiral arrangement of tubes. 



The Ovule. — The ovule is the body attached to the placenta, 



Fig. 446. Pistil of Cynodon Daotylon, a Grass, o. Ovary, s, Feathery stigmas. Fig. 447. 

 1, Perpendicular section of the frond, /, of Riccia glauca, and of the sporangium or spore- 

 case, 0, which is imbedded in it. s. Narrow process or style by which the sporangium com- 

 municates with the external surface. I, Its cavity or loculus. .t, Toung spores still united 

 in sets of four in the parent cells, r, Cells elongated like roots, 2, One of the cells more 

 highly magnified, with the four spores which it contains. Three of the spores are seen, the 

 fourth being concealed by them. Pig. 448. Sporangium or spore-case of Marchantla poly- 

 morpha. o, Hollow swelling containing spores, and which has been compared to the ovary. 

 t, Narrow process prolonged upwards, and resembling a style, jt, Termination of this cellu- 

 lar process, compared to the stigma, c. Cellular covering of the sporangium, or spore-case, 

 surrounding it like a calyx. Fig. 449. 1, Theca or ascus of Solarina saccata, a species 

 of Lichen, containing eight spores, united in sets of two. 2, Two of theSe double spores, 

 highly magniiied. 



