Feb., 1923] CLAYTON — TEMPERATURE AND FUSARIUM WILT 
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The type of wilt characteristic of the Fusarium disease also seems to 
differ from purely mechanical wilting in that there may be a complete and 
rapid killing of tissues and in that cells may regenerate and produce new 
shoots. In these respects it is more nearly comparable to the injuries 
produced in plants by the injection of poisonous compounds. 
Free (4) has noted that the effects of poisonous compounds applied to 
the soil are much localized in the plant, and he suggests that this is due to 
the accumulation of these compounds in certain parts. 
Of more direct interest are the experiments of Rumbold (10), in which 
toxic substances were injected into the trunks of chestnut trees. She 
found that 
The affected region extended up and down the trunk in a line whose width usually 
was but little more than the injection hole. The cells through which the solution passed 
acted like a blotter, with the result that the farther from the point of injection the more 
dilute was the solution and the smaller the injection stream. 
And again, in a later publication (11), 
When a “killing” solution was injected the path was marked on the bark by vertical 
strips of dead tissues. Those twigs and branches whose vascular system entered this path 
were killed; often but one side of the branch was affected. 
Gray (5) has found that many substances produce toxic effects when 
injected into tobacco stems. He found that in this herbaceous plant the 
localization of effects was quite as striking as in the case of the chestnut. 
Thus, a poisonous substance injected into one side of the stem passed up 
the stem rapidly and affected the leaves directly in its path; the lateral 
diffusion, however, was very slight. It was very common to find half a 
leaf killed and the other half remaining healthy, this effect being readily 
produced by injecting the poison just below and at one side of the petiole. 
In all cases there was marked discoloration of the bundles, and only paren¬ 
chymatous tissue in immediate proximity to these browned bundles showed 
the toxic effect. 
Thus the toxic effects of injection of poisonous'substances and the 
killing of host tissues caused by the invasion of F. lycopersici appear very 
similar. It has been demonstrated by experimental work that with a warm 
soil temperature and a cool air temperature the infection of the plants 
takes place readily, the entire vascular system of the tap root and lower 
stem becoming infested with fungal hyphae and badly discolored. The 
cool air, however, prevented the fungus from extending up into the aerial 
parts, which remained apparently healthy both externally and internally, 
the plants making an excellent growth. 
As to the nature of this toxic substance, there are several possibilities. 
It may be that it is a specific secretion of the fungus, or it may be a substance 
formed through the interaction of the host and the parasite. It has been 
amply demonstrated that even so-called normal root excretions removed in 
leaching may stunt plants grown in soil watered with these leachings. 
