MORPHOLOGY OF THE MOLDS 



55 



definite cell walls forming spores. The spore case is 

 termed a sporangium. The structure reaching to the in- 

 terior is a columella, and the stalk upon which the sporan- 

 gium is borne a sporangiophore. In some species the 

 sporangiophore may branch, each branch bearing a terminal 

 sporangium. When ripe the sporangium walls break and 

 spores are scattered. 



Conidia. — Asexual spores of molds not bearing sporangia 

 are frequently termed conidia. Asexual spores may be 

 developed on specialized branches or by changes occurring in 

 the vegetative cells of the mycelium. 



Fig. 36. — ^Development op spokes and spobanoia of Mucoe. 1. 

 Young sporangium with numerous nuclei. 2. Segmentation of 

 protoplasm. 3. Segmentation of protoplasm and separation of 

 spores. 4. Mature sporangium. (Adapted from Blakeslee.) 



Chlamydospores are asexual spores having a relatively 

 thick cell wall. O'idia are developed when the vegetative 

 mycelium breaks up into spores without any differentia- 

 tion of special spore-bearing threads. In most molds a 

 definite fertile thread termed the conidiophore is developed 

 to produce the conidia. The conidiophore may be of many 

 shapes and types, sometimes simple, sometimes branched, 

 and sometimes club-shaped. 



Conidia borne on the tip of branches may be developed 

 in one of two ways. In some species of molds the tip of 

 the conidiophore pinches off spores one after another; if 

 they stick together a chain is formed in which the spore 



