114 KEPRODUCTION. [CH. VIII 



it grows and bulges into the cavity of that receptacle, 

 filling up a great part of its cavity and forming a 

 structure known as the columella (see fig. 49). The 

 protoplasm, remaining over after the development of the 

 spores, degenerates into a slimy gelatinous substance in 

 which the spores are embedded. The wall of the spo- 

 rangium becomes brittle and is covered externally with 

 a coating of minute crystals of calcium oxalate. After a 

 time the wall of the sporangium breaks by the swelling 

 of the jelly, and the spores are set free. In this stage 

 the sporangium presents a characteristic appearance : 

 the remains of the wall look like a broken fringe or 

 cup at the top of the stalk or spore-bearing hypha, and 

 is called the collar: and on the columella (now fully 

 exposed) are usually seen a few scattered spores ad- 

 hering. 



The cycle has now been completed, the spores will 

 germinate, they will give rise to a fresh mycelium, bearing 

 sporangia which contain spores ; and thus the plant may 

 be indefinitely reproduced. 



Mucor. Sexual reproduction. 



Mucor also has a simple form of sexual reproduction. 

 In the higher plants, as in animals, the male element is a 

 structure strikingly different from the egg-cell, which it 

 fertilises. This is obvious in animals where the spermato- 

 zoid is the fertilising agency ; also in the fern where a 

 similar motile male element, the antherozoid, conveys 

 the fertilising element to the egg-cell. But in Mucor 

 there is no such differentiation, the act of fertilisation is 



