INJURIES INDUCED BY PLANTS 55 



may not be possible to apply any practical remedies. It is by 

 no means the first duty of science to call attention to the 

 practical value of a new discovery ; nor should research be 

 primarily directed to those fields which promise to yield results- 



FIG. 12. Decomposition of spruce-timber by Polyporus borealis. a, a tracheid con- 

 taining a strong mycelial growth and a brownish yellow fluid which has originated 

 in a medullary ray ; at b and c the mycelium is still brownish in colour and 

 very vigorous. At d and e the walls have already become much attenuated 

 and perforated ; here the mycelium has been less abundantly supplied with nutri- 

 ment and the filaments are very delicate ; at f the pits are almost completely 

 destroyed ; at g and h only fragments of the walls remain. The various stages in 

 the destruction of the bordered pits are to be followed from i to r ; at i the 

 bordered pit is still intact ; at k the walls of the lenticular space have been largely 

 dissolved, their inner boundary being marked by a circle ; at / one side of the 

 bordered pit has been entirely dissolved ; at m and n one sees a series of pits 

 which have retained a much-attenuated wall on one side only namely, on that 

 which is provided with the closing membrane. In making the section a crack 

 has been formed in this wall. Between o and r both walls of the pits are found 

 to be wholly or partially dissolved, only at/ and q has the thickened portion of 

 the closing membrane been preserved ; at s the spiral structure of both cell-walls 

 is distinctly recognizable. These walls when united form the common wall of 

 the tracheid ; at / hyphse are seen traversing the tracheids horizontally. 



capable of immediate conversion into hard cash. The duty 

 of science is nobler and higher than that. But if, in our 

 search, we succeed in fathoming the mysteries of nature, and, 

 at the same time, obtain results of practical value to humanity, 



