496 BOTANICAL GAZETTE [june 



fumigations, is very interesting. In the data T represents an 

 empirical measure. 



Fumigation strength in cm. Reducing substance 



KCN per cubic foot CONTENT 



o . 003 T7.5 



o . 004 T 8 



o . 005 T 8 



o . 006 T8.S 



0.007 ^ 



0.008 point of first injury T 4 



o . 009 T 3.5 



o.oio ^35 



0.012 T2.S 



0.016. T 2 



0.020 ^ ^ ■ 5 



The sudden drop at the point of first injury was very noticeable; 

 thus from T 9 to a value less than half. Considering this drop as an 

 index of chemical changes, it agrees well with the results of the 

 growth experiments recorded at the beginning of the paper. Every 

 indication was found, also, that the action of the cyanide, at a 

 concentration just below the point of external injury, was radically 

 different from its action at and beyond this point. 



There are two main types of injury resulting from cyanide 

 fumigation: (i) the killing of definite areas of leaf and, much more 

 rarely, stem tissue. This injury is always locaHzed on the younger 

 portions of the plant. (2) Injury in the form of an epinastic 

 response. This is frequently found in cases where the fumigation 

 was just a trifle too strong. As a rule, under these circumstances, 

 there is no apparent injury to the plants for a period of 5-7 days 

 after the fumigation, and then a twisting of certain leaves (epinasty) 

 becomes apparent. This kind of injury is quite distinct from the 

 distortion which arises through an excessive kilhng of tissue. 



The drawings in fig. i were secured after fumigating, with a 

 damaging strength, a house containing tomato plants of different 

 ages. The movement of the injury from the inner portions of the 

 leaf in the old plants to the outer portions of the leaf in young 

 plants was noticeable. The drawings show all the injured leaves 

 from representative plants. Even with the very large plants the 

 injury did not extend below the third or fourth leaf from the tip. 



