670 INSECTS AFFECTING VEGETATION 



gallons of water. Soak the potatoes in this solution for one and one- 

 half hours, after which spread out in the sun to dry before they are 

 cut for seed. This treatment not only kills the Rhyzoctonia fungus, 

 but it also destroys the fungus which produces potato scab and pro- 

 tects the seed potatoes from rotting in the soil, should sprouting be 

 delayed by long continued wet or cold weather. 



In the experiments of the Wyoming Station, we found that 

 treating the seed with corrosive sublimate greatly increased our crop. 

 Care must be taken in using this treatment, because corrosive subli- 

 mate is a deadly poison. It must be used in wooden or earthenware 

 vessels, and these, or the sacks in which the potatoes are placed, must 

 not be used for any other purpose. The solution must not be too 

 strong, nor the potatoes soaked longer than the time stated, because 

 it is apt to kill the potato sprouts, or make them very slow to come up. 

 (Wyo. Press Bui. 16.) 



After soaking the seed, it should be treated with sunshine for a 

 few days, and cut not more than a day or two before planting. Our 

 best results have been obtained by planting small potatoes whole, or 

 by quartering the potato lengthwise, leaving a part of the seed-end 

 on each piece. Plant a liberal amount of seed. (Wyo. E. S. B. 

 [Press] 16.) 



RESISTANT VARIETIES IN THE CONTROL OF PLANT DISEASES. 



The subject of resistant or immune varieties in the control of 

 plant diseases has recently become a prominent one with plant pa- 

 thologists and with many cultivators. It is easy to see what great in- 

 terest it has to those working to keep our crops in health and produc- 

 tiveness for if we can grow crops that are not subject to the common 

 ailments that so reduce the yield annually and periodically almost 

 entirely wipe out a crop ; then all the great trouble of spraying and 

 all other methods and anxieties for crop protection are entirely done 

 away with. 



Undoubtedly most of you have noticed years ago that some 

 varieties of fruits or vegetables rot, or blight worse than others, or 

 what is a closely related phenomenon familiar to all, some varieties 

 are injured by frost much more easily than others and some are 

 more subject to drouth injury than others, that is, some are hardy 

 and others are not. Several years ago, so called immune varieties 

 were put on the market and we had rust-proof oats and blight-proof 

 pears, and while they may have been less subject to these diseases, 

 experience soon proved that they could not be called proof or in> 

 muned from them. 



The theory of immunity and infection in plants (as well as 

 animals) as stated by Prof. Ward and other prominent authorities 

 and supported in fact, at least with certain rusts on grasses, by 

 numerous experiments by Prof. Ward is about as follows: Infec- 

 tion depends on the power of parasites by means of toxins or en- 

 zemes that they produce to overcome the living plant upon which 

 they may be growing, and so feed upon it. Resistance or immunity 

 depends upon the power of the host plant to form anti-bodies (or 



