DISEASES OF TAXODIUM AND LIBOCEDRU8. 



on their hosts and those which live for a longer or shorter 

 period with their host without producing such effect."* 

 To the first class belong all such plants as produce imme- 

 diate death, like Peronospora, Agaricus melleus and many 

 Polyporei, and those producing hypertrophies, such as 

 Gymnosporangium, Exoascus, and others. To the second 

 class belong many Uredineaesaid Ustilagineae,Exobasidium> 

 etc. In the latter cases the mycelium may live for a long 

 period in the cells without any perceptible effect on them. 

 The reason for this "conservation" (Tubeuf, 1. c.) is 

 doubtless to be sought in complex chemical conditions which 

 bring about one kind of effect with one, and another with a 

 different fungus. 



In all the cases just mentioned, one is dealing with living 

 tissues capable of reaction of some sort. This reaction 

 may take the form of starch accumulation, hypertrophied 

 structures or the formation of products antagonistic to the 

 growth of the invading fungus. The bacteria are a good 

 example of organisms bringing about the last form of reac- 

 tion, i. e., where the host produces substances which 

 neutralize the poisonous products formed by the parasite. 

 To what extent similar processes take place in plant cells is 

 yet unknown, but there seems to be no reason why they 

 should not. 



In the heartwood of a tree one is dealing with a plant 

 member to all intents and purposes dead, i. e., its power to 

 react to any stimulus has been lost, so that such influences 

 as would affect the distribution as well as chemical activi- 

 ties of a mycelium in a living member can have no bearing 

 here. There is in the Taxodium a marked localization, 

 and, as will be shown, this is also present in Libocedrus 

 decurrens, Juniperus Virginiana, J. Bermudiensis, and to 

 some extent in pines attacked by several of the Polyporei. 



The localization of chemical action, for such the disinte- 



* Tubeuf, C. Freiherr von. Diseases of plants 21. 



33 



