xviii HISTOLOGY OF MUSHROOM 193 



vestigatecl by cutting thin sections of various parts and 

 examining them under a high power. 



Such sections show the whole mushroom to be composed 

 of immense numbers of closely interwoven, branched hyphae 

 (b) divided by numerous septa into cells. In the stalk the 

 hyphae take a longitudinal direction ; in the pileus they turn 

 outwards, passing from the centre to the circumference, and 

 finally send branches downwards to form the lamellae. Fre- 

 quently the hyphae are so closely packed as to be hardly 

 distinguishable one from another. 



At the surfaces of the lamellae the hyphae turn outwards, 

 so that their ends are perpendicular to the free surfaces of 

 those plates. Their terminal cells become dilated or club- 

 shaped (b, c, a), and give off two small branches or sterig- 

 mata (c, s/g), the ends of which swell up and become 

 constricted off as spores (sp). ^ These fall on the ground and 

 germinate, forming a mycelium from which more or fewer 

 mushrooms are in due course produced. 



Thus in point of structure a mushroom bears much the 

 same relation to Penicillium as Caulerpa (p. 175) bears to 

 Vaucheria. Caulerpa shows the extreme development of 

 which a branched non-cellular organism is capable, the 

 mushroom how complicated in structure and definite in 

 form a simple linear aggregate may become. 



^ Fusion of a pair of nuclei in the young club-shaped cell or basidtum 

 precedes the nuclear division which provides a single nucleus for each 

 s^K. — W.N.P. 



