SPORE FORMATION 399 



According to Lafar, the mycelium may, therefore, be defined as 

 that portion of the thallus of the mould which is spread out on the 

 culture soil and which derives from it the nutrition necessary for the 

 organism. The mycelium arises from a spore which has been im- 

 planted upon or within a favorable culture soil. From the spore one 

 or several germ sacs are formed ; these grow elongate, divide, and form 

 the individual hyphen or mould filaments which in their entity compose 

 the mould mycelium. The latter always grows at the external ends 

 of the individual hyphens and not at the end which originally arose 

 from the spore. In this respect the eumycetes differ from the schizo- 

 mycetes, which grow at both ends and in multiplication divide in the 

 middle. In the study of the mycelium two types are noted, one in 

 which the whole mass, much branched and complicated as it may 

 be, consists of a single cell only; the other in which the hyphens, or 

 filaments, are divided by septa into cylindrical segments, which by 

 their union form the hyphens. Moulds of the first type are classified 

 as phycomycetes; those of the latter as mycomycetes. The fructifying 

 organ is also developed in all hyphomycetes, though in the lowest 

 forms it may be rather rudimentary and inconspicuous. The function 

 of the fructifying organ is the production of cells from which new 

 individuals can be formed. Such cells of lower plants, as has already 

 been stated in the consideration of bacteria, are called spores. A 

 bacterium, however, almost invariably forms a single spore only, 

 while hyphomycetes generally form a large number of spores. 



Spore Formation. Four different varieties of spore formation are 

 recognized in hyphomycetes, namely: 



1. Endospores, or gonidia. 



2. Zygospores 



3 Exospores, or conidia. 



4. Chlamydospores, or gemmae. 



The first three types of spores are formed by the fructifying organ, 

 except among the very lowest type of hyphomycetes, where the cells 

 of the mycelium form the spores in their interior without any pre- 

 liminary differentiation. This mode of formation is like that in 

 bacteria, only that it is generally a multiple and not a single spore 

 formation. 



1. ENDOSPORES, OR GONIDIA. In the formation of the fructifying 

 organ one or several hyphens arise from the mycelium and grow 

 upward, becoming straight and much stronger than the ordinary 

 mycelial hyphens or filaments. This stem is called the fruit bearer, 

 or fruit carrier. Its upper free end becomes globularly or elliptically 

 enlarged, and in this extremity the spores are formed after it has 

 become separated from the remainder of the stem by a straight or 

 curved septum. This free round or oval separate end forming the 

 spores is now called a sporangium, while the stem which carries 

 the latter is often called the columella (the little pillar). This is the 

 mode in which endospores or gonidia are generally formed. 



