164 SAPROPHYTIC FUNGI 



mycelium (even from the same branch) will conjugate, 

 and in these zygotes are commonly found. In other 

 kinds zygotes are much rarer, since conjugation will 

 only occur between hyphse of two different " strains," 

 one of which grows more vigorously than the other. 

 Here we have a functional differentiation between the 

 conjugating hyphae which is not quite on a par with, 

 but shows an interesting parallel to, the ordinary sex- 

 differentiation, the essential characters of which we 

 shall have to consider in Chapter XII. 



Penicillium (Blue Mould). — This is a common form 

 growing on substances similar to those on which 

 Mucor occurs. It forms the well-known mould of 

 Stilton and Gorgonzola cheese. The mycelium differs 

 from that of Mucor in being septate, i.e. there are 

 cross walls at intervals, dividing the mycelial tube 

 into multinucleate compartments. The characteristic 

 blue-green pigment is distributed through the cyto- 

 plasm, and has nothing in common with the chlorophyll 

 of a green plant. 



Spore Formation : Conidia. — Upright, aerial hyphae 

 arise from the mycelium as in Mucor, but instead of 

 forming sporangia, each forms several branches at 

 the same level, the branches continuing the same 

 general direction of growth but diverging shghtly 

 from one another. At a certain height each of these 

 branches again in the same way, so that a sort of 

 compound pencil of hyphae is formed with the tips 

 of their ultimate branchlets close together on the same 

 level. From the tips of these branchlets minute 

 spores called conidia are budded off, and before each 

 is quite detached another is budded off behind it, so 

 that a series of parallel or nearly parallel chains of 

 conidia are produced (Fig. 16, j). These are very 



