14 GENERAL MORPHOLOGY. 



§ 220.— Fructifleation by Sporangia. 



The separation of the thallus into two portions : the mycelium 

 on the one hand, and the organ of fructification on the other, 

 can be readily found in all Eumycetes of anything like a high 

 stage of development ; though in the lower members of the 

 system they are only very indefinite ; and may even be entirely 

 absent, in which case the mycelium itself is converted into an 

 organ of fructification. 



The chief function of the organs of fructification is the pro- 

 duction of structures capable of developing into new individuals 

 of the same species as the parent organism. In the case of 

 fungi these structures, which consequently serve for direct pro- 

 pagation, are termed spores ; and, in accordance with the method 

 of their production, are divided into four groups : — 



(i) Endospores, or Gonidia. 



(2) Zygospores. 



(3) Exospores, or Conidia. 



(4) Ghlamydospores, or Gemmve. 



Setting aside, for the present, the fourth group, which occu- 

 pies a position apart, it may at once be stated that, in all the 

 more highly developed Eumycetes, spores of the other three 

 groups are produced by a special organ, which branches off from 

 the mycelium as a fruit-bearing stem : the aerial hypha. 

 According to the species of the fungus and the external con- 

 ditions, each of these stems may produce either one or more 

 spores. 



To take first the case of the Endospores : these, as the name 

 implies, are formed within the fruit-bearing oi^gan, or a special 

 part thereof. Except in the very lowest species of endosporo- 

 genic Eumycetes, in which the mycelium itself is converted into 

 an organ of fructification, and its contents into spores, the pro- 

 cess takes its course along the following main lines : an upiight, 

 aerial hypha (see Fig. 91) branches off from the mycelium, and, 

 as it proceeds to attain full growth, enlarges at the upper ex- 

 tremity to a usually spherical or bottle-shaped bubble : the 

 si>orangium, so called because in it the spores are formed. Be- 

 fore this happens, however, a septum is developed between the 

 sporangium and the aerial hypha, which wall, in many cases, is 

 not straight but curved, and projects some distance within the 

 sporangium, as though actually au enlargement of the tip of the 

 hypha. In some instances it assumes the form of a short pillar 

 (Fig. xoo), on which account it has received the general name 

 columella. The endospores are then foi-med, as free cells, out of 

 the contents of the sporangium, either the whole of these con- 

 tents being drawn upon for this purpose, or only a portion as in 



