154 Toxic Action of Traces of Coal Gas upon Plants 



upon endodermal development. The mechanism for the normal pro- 

 duction of the Casparian strip appears to require two factors: (1) a cell 

 membrane in a specially receptive chemical state; (2) diffusing unsaturated 

 fatty acids. The cell membranes appear to be found in the necessary 

 state only when recently differentiated, and in the presence of oxygen. 

 When cork tissue is forming, the cells are laid down by a meristem, 

 the walls of which can be shown to have many properties in common 

 with those of the meristem at a growing point. As the cells are cut 

 off to the outside they are in contact with oxygen, and at the same 

 time fatty acids are deposited in them and undergo transformation 

 into suberin (Priestley (13), Priestley and Woffenden(ii e)). If these acids 

 are unsaturated, then their deposit in these membranes may well be 

 hindered in the presence of gaseous unsaturated hydrocarbons. Under 

 these conditions, the walls would remain unimpregnated with fatty acids, 

 and would be readily distended, giving rise to the proliferated tissue so 

 frequently reported in cases of gas poisoning. The tissue formed under 

 these conditions would be extremely fragile, and as it formed at the base 

 of the normal bark, the strain, engendered by the expanding tissue within, 

 would cause shearing in these weak layers resulting in the development 

 of cracks in the bark. An experimental investigation into the truth of 

 these suggestions is now in progress. 



Summary. 



1. There is clear evidence in the literature that the toxic action of 

 traces of illuminating gas upon plants may be traced to the presence 

 of gaseous unsaturated hydrocarbons, A concentration of one part of 

 ethylene in ten million of air is toxic to the etiolated epicotyl of a pea. 



2. The effect of these unsaturated hydrocarbons can be traced in 

 the case of root or etiolated stem to their inhibition of the formation 

 of a functional primary endodermis, which is usually present in these 

 plant structures. 



3. The unsaturated hydrocarbons prevent the formation of a 

 functional endodermis, by preventing the normal accumulations of 

 unsaturated acids in the region of the future Casparian strip. 



4. It is suggested that the effect of traces of these gaseous un- 

 saturated hydrocarbons upon cork formation may be due to the arrest 

 of the normal deposit of fatty acids in the membranes of the cork cells. 



5. The practical significance of this work lies in the fact that definite 

 diagnostic features may now be sought for when injuries to plants are 

 suspected to be due to gas poisoning. 



