358 JouriiA of AgricuItKrc. [10 June, jpio.- 



soil mav possess, not onlv against actions of this kind, but also against 

 the presence of poisonous or injurious organi : or inorganic substances in 

 the soil. 



To conclude, the facts mentioned above mav be summarized as 

 follows : — 



1. In most soils, and particularly in virgin soils, the proper working 

 of the soil is usuallv far more important than is its manuring. 



2. Water is the plant's most important requirement and it cannot be 

 replaced in the slightest degree by any other factor, whereas a deficient 

 mineral food element mav in part be covered or replaced by a surplus cf 

 another substance of which the plant does not need so much as is present, 

 or which it does not use at all under ordina.ry circumstances. 



3. Each essential factor can .set a limit to the growth of the crop however 

 well all the others may be .satisfied. Hence, to add mineral manures to a 

 soil where the stunted growth is due to a deficiency of Avater is more likely 

 to retard growth than to increase it. 



4. The limiting factors to growth need to be separatelv determined 

 in each case and the answer will depend upon the crop, upon the soil, upon 

 the climate and upon the rainfall. 



5. It is when the failure of a crop is due to the deficiencv of a single 

 factor that its satisfaction by irrigation, bv soil treatment, or by manuring^ 

 as the case may be, will produce the most striking and profitable results. 



TESTIXG POTATO VARIETIES FOR IRISH BLK^HT. 



D. McAlpiiie, Vegetable PatJwlogist. 



It is a wise pro\ision of the Federal Quarantine Aei that potatoes are 

 not admitted to the Commonwealth from any country where the Irish Blight 

 is known to exist, and this might seem at first sight to shut out any promis- 

 ing new varieties which it might be found desirable to introduce for 

 experimental purposes. But, from the knowledge we now pos.sess of this 

 disease, it is quite possible to test under .strict quarantine conditions anv 

 new variety, so as to determine whether there is anv risk of introducing 

 the blight with it. 



It is an established fact that the only known means of importing this 

 disease from countries separated from us by a wide expanse of ocean, is 

 in the potato itself. The spawn or mycelium of the fungus causing this 

 disease must be dormant in the tubers before there is any pos.sibility of 

 its development, and fortunately we are able, not only to detect its presence, 

 but to destroy it even when concealed in the tissues of the potato. The- 

 destructive agent is dry heat and this is applied in such a way that the 

 sprouting of the potato is not interfered with ; in fact, it is rather 

 stimulated than otherwise as numerous experiments have shown. By grow- 

 ing potatoes submitted to this treatment in a quarantine area for at least 

 two years there would be a complete safeguard against any ix)ssible con- 

 tamination from this source. 



The method has already been tested on the Continent of Europe- 

 by Jen.sen, who used freshlv dug di-seased tubers and found that the 

 fungus was destroyed in the treated potatoes, while those untreated 

 developed a rich crop of the fungus. I have also carried out similar 

 experiments and obtained similax results. Diseased potatoes were placed 

 in an incubator for four hours, kept at a constant temperature of 120 deg. 



