REPRODUCTION 68 1 



may be cylindrical or club-shaped. One important and 

 specialised type of sporangium containing a definite limited 

 number of spores is termed an ascus {C, Fig. 255). 



(ii) A conidium (c and b, Fig. 229) is a simple cell of very 

 variable form and dimensions, cut off or abstricted from the top 

 of a hypha, the latter being termed the conidiophore (a, Fig. 229). 



It would appear from comparative study that a conidium 

 represents a degenerate one-spored sporangium, the spore case 

 and the spore within it having become a single structure. 



Frequently as soon as one conidium has been formed, others 

 are produced behind it in succession from the same hypha ; thus 

 chains of them may arise. 



All conidia are at first single cells, but they sometimes become 

 multicellular by the formation of dividing-walls (Figs. 236 and 

 237), and in such cases each new cell subsequently behaves as 

 a separate spore. 



A special form of conidiophore characteristic of a large group 

 of the higher fungi is termed a basidium, the conidia borne upon 

 it being known as basidiospores (s, Fig. 252). 



(iii) Among fungi of many different orders the hyphse forming 

 the mycelium often become divided by transverse walls into a 

 large number of short segments, each of which is capable of 

 germinating and giving rise to a new plant ; these segments, 

 which may remain united in chains, or become free from each 

 other, are known as ot'dia. 



Between oidia and chlamydospores no strict line of demarcation 

 can be laid down. The latter, however, are generally thick-walled, 

 usually brown or dark-coloured spores, frequently intercalated 

 or produced at irregular intermediate points along a hypha, but 

 sometimes occurring at the apex of the latter. On germination, 

 they often give rise to short hyphse, bearing either sporangia or 

 conidia (Figs. 240, 242 and 243). 



6. In the simplest fungi the spores are borne directly on the 

 mycelium, but in a great many species there exists a special 



