222 PLANT LIFE. 



316. Simple sporangia. — The simple sporangium may 

 be like the general body-cells, or it may be specialized in 



Fig. 220. — Longitudinal section of the simple sporangium of a mold (Mttcor). The 

 aerial hypha, //, has partitioned off a cell, .r, within which spores are produced. The 

 walls of this sporangium are studded with needle crystals of calcium oxalate. The par- 

 tition protrudes far into the end cell. Magnified 260 diam. — After Kerner. 



Fig. 221. — Longitudinal section of the stem, s, of a moss gametophyte, bearing leaves, 

 b. Embedded in the stem is the sporophyte, consisting of a stalk, st , and a compound 

 sporangium, of which w is the wall, formed of a sheet of cells, enclosing the spores, 

 sp (contents not shown). Magnified 100 diam. — After Hofmeister. 



form as well as in function. It may be spherical, sac-like, 

 or linear. The elongated sporangium produced by the en- 

 largement of the end of a hypha in certain fungi has received 

 a special name, ascus. The number of spores formed within 

 a simple sporangium may be two or more, up to several 

 hundred. The spores are formed like the zoospores de- 

 scribed in ^[ 306, with the difference that a wall is secreted 

 by each spore be/ore it escapes. 



The rupture of the tell wall, which sets the spores free, 

 is brought about by the increase of the spores in size, or by 

 the swelling of the surplus protoplasm left after their forma- 

 tion. Preparatory to bursting, the wall is frequently altered 

 so as to be mucilaginous, or it becomes brittle. In some 

 cases a certain area is thin, which furnishes a starting-point 

 for the rupture. 



