46 EXPERIMENT STATION. [Jan. 



These substances are to be found in the tissue, although, as al- 

 ready pointed out, the reactions are not quite the same in differ- 

 ent places nor on different species of trees. Trees poisoned by 

 illuminating gas usually show some characteristic post-mortem 

 symptoms, but many of these symptoms may be found in trees 

 dying from other causes. More or less rapid deterioration and 

 increased brittleness of the wood is a quite characteristic symp- 

 tom, however. 



In summer the first effects of gas poisoning may be seen in 

 the foliage. The leaves turn yellow and in some cases drop off, 

 while the leaves of other trees fall while still remaining green, 

 and in still other cases the trees do not become defoliated but 

 the leaves turn a reddish brown and die. The upper part of 

 the tree, being far away from the source of water supply, 

 usually shows the effects first. All this occurs before there is 

 any evidence of abnormal tissue above ground. The water con- 

 tents of the soil containing the poisonous principles of gas pass 

 up through the roots and stems, and later the wood and zone 

 constituting the living portion of the trunk become abnormal. 

 The first symptoms appear in the characteristic dryness of the 

 cambium and other tissues outside the wood, this being the first 

 indication of the approaching death of the tissue. Later these 

 tissues, — cambium, phloem and cortex, — turn brown and dis- 

 integration follows. These abnormal conditions first take place 

 in the roots, which are the first to absorb the poison, but later, 

 as absorption and translocation proceed, the poisonous constit- 

 uents may be detected in the wood, etc., at the base of the tree. 

 It not infrequently happens that the tissue at the base of the 

 tree is dead, while that in the trunk a few feet above is alive. 

 But this condition does not endure, for sooner or later the whole 

 tree becomes involved. When the underlying tissues, cortex, 

 phloem, etc., die, the bark changes color, gradually growing 

 darker, the tissue tensions are destroyed, and the physical prop- 

 erties of the bark are greatly changed. Soon various species of 

 fungi, such as Folysiictus, ScJiizophyllwn and others, find a 

 foothold on the bark and borers and other insects attack the 

 dead tissue. Even bacteria and molds, like PenicUlium, be- 

 come active and hasten the process of disintegration, the smaller 

 twigs becoming dry and brittle, and the ends are often broken 



