MISSOURI BOTANICAL GARDEN. 



fibers without any impurities whatever. The quantity of 

 wood transformed into cellulose is exceeded only, as far as 

 I know, by that found in diseased wood of Juniperus, 

 decayed by Trametes Pini, to be described in another 

 paper. 



With polarized light, the prisms being crossed, the pri- 

 mary lamella of sound wood appears white, i. e.,itis 

 highly refractive ; the secondary lamellae are darker. The 

 rotted wood, with the exception of some very minute parti- 

 cles, allows no light to pass. The hypothesis of a crystal- 

 line structure of the cell-wall, as advocated by Nageli, is 

 based largely on its optical properties. Nageli held that 

 the double refraction indicated a condition of stress in more 

 than one direction. The absence of any refraction in the 

 rotted wood indicates a homogeneous condition, i. e., one 

 in which the stress is equal in all directions. The change 

 from sound wood to the decayed form must have been a 

 profound one to bring about this condition. It has been 

 noted for wood destroyed by Merulius lachrymans ,* that it 

 separates the white polarized light into blue and yellow 

 parts. Hartig makes no attempt to explain why this should 

 be so. In this connection it may be said that rotted wood 

 of Libocedrus decurrens, yet to be described, and wood of 

 Juniperus Viginiana destroyed by Polyporus carneus, 

 appear dark when viewed with crossed prisms. 



HUMUS COMPOUND. 



In the cells immediately surrounding the rotted areas 

 certain parts of the walls are colored dark brown by an 

 apparently homogeneous substance. This occurs in various 

 forms. Most commonly it has numerous cracks and fissures 

 breaking it into many plates, looking much like mud which 

 has dried in the sun (PL 4, fig. 4), then again it appears 

 in the form of irregular granules scattered along the walls, 



* Hartig, R. Der achte Hausschwamm 61. Berlin. 1885. 

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