GENERAL CHARACTERS 157 



threads projecting from the surface of the mouldy substance ; 

 and these free filaments (Fig. 37, A, a. hy) can be easily 

 ascertained to be connected with others (my) which form a 

 network ramifying through the substance of the bread or 

 horse-dung. This network is called a mycelium ; the threads 

 of which it is composed are mycelial hyplm ; and the fila- 

 ments which grow out into the air and give the characteristic 

 fluffy appearance to the growth are aerial hyp/ice. 



The aerial hyphae are somewhat thicker than those which 

 form the mycelium, and are at first of even diameter through- 

 out : they continue to grow until they attain a length, in M. 

 mucedo, of 6-S cm. (two or three inches). As they grow 

 their ends are seen to become dilated, so that each is termi- 

 nated by a minute knob (A, spg) : this increases in size and 

 darkens in tint until it finally becomes dead black. In its 

 earlier stages the knobs may be touched gently without 

 injury, but when they have attained their full size the 

 slightest touch causes them to burst and apparently to dis- 

 appear their actual fate being quite invisible to the naked 

 eye. As we shall see, the black knobs contain spores, and 

 are therefore called sporangia or spore-cases. 



Examined under the microscope, a hypha is found to be 

 a delicate more or less branched tube, with a clear trans- 

 parent wall (B, c. w) and slightly granular contents (plsm) : 

 its free end tapers slightly (H), and the wall is somewhat 

 thinner at the extremity than elsewhere. If a single hypha 

 could be obtained whole and unbroken, its opposite end 

 would be found to have much the same structure, and each 

 of its branches would also be seen to end in the same way. 

 So that the mould consists of an interlacement of branched 

 cylindrical filaments, each consisting of a granular substance 

 completely covered by a kind of thin skin of some clear 

 transparent material. 



