56 



BOTANY. 



formed about each one, and at the same time the columella and the stalk 

 of the sporangium become dark- colored. 



When ripe, the wall of the sporangium dissolves, and the spores (Fig. 

 32, E) are set free. The columella remains unchanged, and some of the 

 spores often remain sticking to it (Fig. 32, D). 



FIG. 32. ^!, common black mould (Mwcor), x 5. B, three nearly ripe spore 

 cases, x 25. C, development of the spore cases, i-iv, x 150 ; v, x 50. Z), spore 

 case which has discharged its spores. E, spores, x 300. F, a form of Mucor 

 miicedo, with small accessory spore cases, x 5. G, the spore cases, x 50. H, a 

 single spore case, x 300. I, development of the zygospore of a black mould, 

 x 45 (after DeBary). 



Spores formed in a manner strongly recalling those of the pond scums 

 are also known, but only occur after the plants have grown for a long 

 time, and hence are rarely met with (Fig. 32, 7). 



Another common mould (M. mucedo), often growing in com- 

 pany with, the one described, differs from it mainly in the 

 longer stalk of the sporangium, which is also smaller, and in 

 not forming runners. This species sometimes bears clusters of 

 very small sporangia attached to the middle of the ordinary 



