224 PLANT LIFE. 



sarily ruptured to permit the escape of the spores, being 

 often displaced in the development of the sporangium, so 

 that at maturity it is partially free. 



Fig. 223. — A mildew {Erysiphe communis), showing the mycelium ramifying over a 

 bit of leaf, with erect spore-bearing branches and globular fructifications, containing 

 asci. Magnified about 175 diam. — After Tulasne. 



318. Compound sporangia. — Simple sporangia occur only 

 among the lower plants. In the higher plants, including 

 the mossworts, fernworts, and seed 

 plants, the sporangium is always 

 compound. 



319. Development. — Compound 

 sporangia may be developed either 

 from superficial or from internal 

 Fig. 224— a cluster of asd from cells. As a consequence, the mature 



the interior of the fructification ^ 



of a mildewi J ffryji>A*//^r« < :/?i) S p 0ran gi a w ju be either free or more 



similar to those shown in fig. 223. l ° 



Each ascus contains four spores. or } e sS enclosed within the tissues of 



Magnified 200 diam.— After De- 



Baf y- the organ by which they are borne. 



A superficial cell may enlarge so as to protrude from the 

 surface, and divide into two parts, of which the upper cell 

 develops into the sporangium proper, and the lower cell into 

 its stalk. According to this method of development the 

 sporangium is a surface appendage, and may be looked upon 



