1890.] NEW-YORK MICROSCOPICAL SOCIETY. 113 



around and throitg/i the limb, but also to rid itself of the useless 

 member. The cells of the cambium layer of the branch no 

 longer being active those of the trunk are rolled out, pressing 

 firmly against the lower, right and left sides of the branch, over 



:;'/»;// ';/. V//;f«H . V.,V ,,» , '"e "PPer side, or .he ..v///,, of 

 ////y ' ' ' -^ ^Mi|f the branch, the expanding cam- 



bium layer would be separated 

 for a short distance, leaving a 

 triangular, or heart-shaped space. 

 To close up this space is the 

 function of the spiral, or ellip- 

 tically wound tracheids. At 

 first there is usually but one 

 '' series ; but as the tree increases 

 / in diameter, and the branch is 

 / compressed in- diameter, a sec- 

 '/ nnd, and, sometimes, a third 

 ^ series form, as is the case of the 

 White Cedar illustrated. 



Fig. 3. rj,! • ^ • . 



1 his tree growing in swampy 



ground, is a slow grower, and a durable wood. It decays slowly, 

 even when attacked by its special fungus, Agaricus canipanella, 

 Batsch. It takes many years for the wood to grow over the 

 stub of the decayed branch, and in many cases the fungus will 

 work through the stub to the upright cells of the tree, and start 

 a small zone of decay. The increasing spirally wound tracheids 

 check the air supply, eventually cutting it off, eliminating one of 

 the essential conditions in the combination for the growth of 

 the mycelium of the fungus, and further decay of the living tree 

 is arrested. 



Timber cut from the White Cedar often shows many zones, 

 where decay has started and has been subsequently arrested. In 

 all cases these zones of decay have been started around the de- 

 cayed branches, and arrested as described. The mycelium in 

 these zones of decay will remain dormant for years, but will 

 revive if the tree is cut into timber and used, when all of the 

 conditions for the growth of fungi are in combination. Yellow 

 Pine being a more rapid tree to grow than the White Cedar, the 

 stubs of the decayed branches are more quickly overgrown, and 

 we do not find the upright cells of the wood as frequently at- 



