[Vol. 2 



284 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



conclusion that these diseases are not to be controlled by 

 fighting the fungi, but by influencing the potato plant. Though 

 caused by a fungus, the production of the conditions favora- 

 ble to the progress of the disease is attributable to irrigation. 

 In many cases the root system was poorly developed, the dif- 

 ferent kinds of irrigation showing an influence upon the 



growth of the underground parts of the plants. We know very 

 little of the conditions of growth of the potato in spite of a lew 

 publications on this subject by Miiller-Thurgau, De Vries, and 

 Vochting. Moreover, we know nothing about transpiration 

 and water requirements in these plants or about their ability 

 to form roots, or the factors that influence these processes. 

 It is, therefore, very important that Shantz, of the Depart- 

 ment of Agriculture, has actually undertaken the investigation 

 of these problems. Others must follow him as soon as possible 

 to solve these questions for the irrigated lands. 



The chemical-physiological side of the phytopathological 

 questions also needs more attention, as has been pointed out 

 recently by me and others in work upon the freezing problem. 

 For a true judgment of the resistance to frost, in the 

 case of cereal diseases, Gossner has apparently found the 

 right way. The earlier stated fact that the cells of small 

 pieces of tissue floating on a sugar solution are less quickly 

 killed by frost than when floating in water, made it probable 

 that the young plant is protected by sugar against frost in- 

 jury. The investigation of the winter and summer rye shows 

 that the sugar content of the former is several per cent greater 

 than of the latter. The same is the case for frost-susceptible 

 races of wheat. We may thus find out the relative frost re- 

 sistance of closely related races of plants by determining the 

 sugar content. 



But other phases of chemistry are of importance in phy- 

 topathological investigations, as, for instance, the chemistry 

 of colloids, which, as Euhland showed in his work, is of 

 great value. The microchemical reactions are also of great 

 importance. We know today that cork formation in the 

 potato is a protection against bacterial invasion. I could 

 show by using the reaction of Tisson that the deposition of 



