[Vor. 3 
76 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
in the case of cabbage. Moreover, it grows readily at tem- 
peratures much lower than this. The raising of the tempera- 
ture merely increases the rapidity of the growth of the fungus 
and, therefore, as far as this investigation is concerned, the 
high temperature from the standpoint of the fungus aids its 
destructiveness by increased spread in the soil, and more rapid 
development in the vascular system after it has once entered. 
Other possible relations, such as that of production of toxic 
substances, remain to be worked out. 
From the host standpoint the effect of temperature is much 
more complicated. Appel (715) in his discussion of leaf roll 
in potato considered excessive transpiration of prime im- 
portance in bringing about this condition whether the cause 
of the trouble was parasitic or not. The symptoms of the dis- 
ease in the cabbage indicate that the phenomena involved are 
very similar to those concerned with the annual autumn fall 
of leaves from woody plants. The discoloration (yellowing in 
the diseased plants), the formation of an abscission layer, 
and finally the fall of the leaves are in all ways comparable. 
Hence the same physiological changes within the plant are 
probably taking place. From this point of view then, the 
work of Molisch (286) and Varga (711) on the relations of 
environmental factors to the fall of leaves gives a basis for 
an explanation of the symptoms from the host standpoint. 
Molisch showed that a slow but continued decrease of water 
content of the fundamental tissue of the leaf led to the for- 
mation of an abscission layer and finally fall of the leaf. He 
further found that this loss of water might be brought about 
by increased transpiration or by decreased absorption or con- 
duction from the roots to the leaf. Temperature influenced 
leaf-fall, both indirectly through its effect on transpiration, 
and directly by bringing about the formation of the abscission 
layer. Leaves fell at 17-22°С. more rapidly than at 1-10°C. 
when other conditions were equal. Varga studied the relation 
of temperature to leaf-fall more exactly and found that, as a 
rule, low temperatures lowered transpiration and thereby set 
up a stimulus to leaf-fall, but that if the abscission layer 
had been formed through other influences, higher tempera- 
