Mo7'phology. 19 



'^ skin,^' wMcli in dry weather forms a more or less 

 cartilaginous layer, and when wet can often be 

 peeled off as a slimy pellicle. The slime that covers 

 the pileus of many fungi in wet weather, often in such 

 quantities as to trickle away in drops, is also due to 

 the complete gelification or melting of the external 

 hyphge. In perennial fungi, frequently spoken of as 

 woody fungi, on account of the hardness of their 

 tissues, the walls of the hyphge usually become much 

 thickened, and at the same time coloured and 

 cemented together by the partial gelification of their 

 walls, which on again hardening form a tissue as hard 

 and firm as the hardest wood. Such structures are 

 common in the large group known as the Pohjpore^. 

 The above account covers the most usual changes tak- 

 ing place in the sporophore for the purpose of giving 

 greater strength to the structure, but I have described 

 elsewhere ^^ a very remarkable differentiation in the 

 tissue of the sporophore, for the purpose of giving 

 additional strength, met with in a few species of Polij- 

 porus. In Polijporus pisochapani, a fungus having a 

 stem four or five inches long and about half an inch 

 thick, and a pileus about three inches across, the 

 tissue in the young condition is homogeneous and 

 pliable, just a little denser towards the outside, but 

 as the fungus approaches maturity, the tissue of the 

 stem and pileus undergoes a remarkable differentiation 

 as follows : a thin zone of tissue just within the cir- 

 cumference of the stem becomes sharply defined by 

 having the walls of the hyphee thickened by additions 



^ On the differentiation of the tissues in Fungi, Journ. Koy. 

 Micr. Soc, 18S7, pp. 205-208, pi. 1. 



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