140 



DERMAL SYSTEM 



a rather more compact arrangement of the peripheral hyphae, which 

 often also have coloured and more or less mucilaginous walls. The long- 

 lived woody fruit-bodies of various Polypori (P. lucidus, P. fomentarius), 

 on the other hand, are provided with a comparatively tough dermal 

 tissue composed of the thickened ends of hyphae, which are all placed 



at right angles to the surface, so as to 

 form a palisade like layer (Fig. 42 c). In 

 a number of cases the surface of the fruit- 

 body also bears trichomes, which assume a 

 variety of shapes and, presumably, perform 

 a corresponding variety of functions. The 

 so-called sclerotia of Fungi also usually 

 possess a very firm thick-walled epidermis ; 

 the latter appears to consist of one or more 

 layers of " cells," but is in reality made up 

 xkdia.no -, dermal f the peripheral branches of hyphae which 



tissue. x390. After do Bary. " l J r 



further inwards constitute the storage-tissue 

 or 'medulla." In Sclerotinia Fuckcliana, for example, the epidermis 

 (" cortex ") of the sclerotium consists, according to De Bary, 86 of one 

 or two layers of isodiametric " cells," which have tough dark-brown 

 membranes and are very firmly united (Fig. 43, r). In S. sclcrotwrinn 



i 



T.S. 



Fig. 43. 

 through a sclerotium 



Fig. 44. 



Thin T.S. through n ripe sclerotium of Sclerotinia Sclerotiorum, showing multiple 



dermal tissue. 



a multiple epidermis is produced by tangential division (Fig. 44). 

 In certain species of Typhula (T. phacorrhiza, T. gyrans, T. Evpliorbiae, 

 T. g rii ihin u in, etc.) the epidermal cells of the sclerotia are tabular or 

 prismatic in form. The smooth or tuberculate outer walls are very 

 thick, whilst the inner and lateral walls remain unthickened ; the side 





