222 



PLANT LIFE. 



316. Simple sporangia. — The simple sporangium may 

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



Fig. 221. 



Fig. 220. — Longitudinal section of the simple sporangium of a mold {Mucor). The 

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

 walls or 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, */. and a compound 

 sporangium, of which iu 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 before it escapes. 



The rupture of the cell-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. 



