The Biology of Polyporus Pargamenus Fries 111 
From the tests described above in full detail, and from 
still other tests employed for the differentiation of both cel- 
lulose and lignin, it is evident that the vessel walls are by 
far the most strongly lignified of any of the elements. It is 
also evident that the medullary 1 ray and wood parenchyma 
cells, while less strongly lignified than the vessel walls, are 
more strongly lienatied than. the wood prosenchyma elements. 
Of the individual cells the middle lamellz are lignified to a 
much greater extent than their secondary layers of thicken- 
ing. It is further evident that the secondary and tertiary 
layers of thickening of the prosenchyma elements are the 
least lignified tissues of the wood. As a result of the dis- 
similar structure and microchemiecal reactions of the various 
elements we naturally would expect to find that the vessel 
walls would resist decay longer than any other one element. 
Of the other elements the middle lamellee would be more 
resistant to the solvent action of the fungus than the 
secondary layers of thickening possessed by these respective 
elements. It would therefore appear that the secondary 
layers of thickening possessed by the wood prosenchyma ele- 
ments would decay most rapidly. 
Macroscopic Appearance of Decayed Wood.— In its gen- 
eral features the macroscopic appearance of decayed bitternut 
hickory wood is essentially the same as that deseribed for 
yellow birch. The last element to resist decay within the 
individual pockets was the vessels, which evidently were 
strongly lignified. In well-decayed wood the vessels, under 
a hand lens, appear as minute elass tubes lying loosely within 
the various pockets, all the ‘other elements having disap- 
peared long ago. In fact the wood was decayed to ‘such an 
extent that the individual vessels could be removed readily 
with tweezers and used for microscopic study. Numerous 
mycelial strands, running both longitudinally and radially 
through the decayed wood, were readily visible to the 
unaided eye. 
Microscopic Characters of Decayed Wood.— The dissolu- 
tion and course of delignification of the woody elements -is 
