132 



DISCOVERY 



testifying to the value of prompt destruction of refuse, 

 but these must suffice. 



Mention, moreover, should be made of weeds. These 

 are not only injurious directly by crowding out the 

 proper plants and robbing the soil of food material,' 

 but indirectly to a greater extent by acting as hosts 

 for injurious pests and diseases which might other- 

 wise starve before their normal food-plant was 

 growing again in the field. 



Growers are also by no means blameless as regards 

 introducing a pest or disease to their crop. Thus 

 fruit-growers buy trees that are infested with various 

 pests which, by a little care and attention, could be 

 got rid of at an early stage. Seed is sown which 

 carries with it the spores of certain diseases, and plants 

 like cabbages are bought which introduce diseases 

 into hitherto clean soil. Of course the nurserymen or 

 seedsmen are also to blame in such cases, and very 

 shortly it wiU become an offence to sell plants or seed 

 seriously affected with certain scheduled diseases. 

 Many such diseases could be prevented by treatment 

 at an early stage. Thus, cereals suffer frequently 

 from a disease called smut, which causes the ears to 

 produce sooty-like masses in the place of the grain. 

 Suitable treatment of the seed by chemicals, such as 

 formaline or blue vitriol (copper sulphate), will prevent 

 this, and up-to-date farmers always " dress " their 

 seed before sowing. 



The prevention of disease by planting varieties 

 which are immune from, or resistant to a disease, has 

 been dealt with before,^ and little more need be said. 

 Although of partial application only, as the resistance 

 is only to specific diseases, it can be used where a 

 particular pest is rampant, and a crop obtained not- 

 withstanding its presence. 



" Dodging a pest " is also practical in some instances. 

 Certain pests can work only within certain limits ot 

 temperature, moisture, etc., and if these are known, an 

 attack may be prevented. Thus the early sowing of 

 oats may prevent an attack of the frit fiy, which 

 causes much loss, and the late sowing of wheat in the 

 autumn may save a field from attack by one of its 

 parasites. Space prevents further illustrations, but 

 one may conclude with a few words on prevention by 

 preservation of a pest's parasites. The obvious case 

 is the protection of insectivorous birds which feed on 

 insects, the greater proportion of which are injurious. 

 Besides these, there are smaller enemies of insect 

 pests, such as the ladybird-beetles and their larv;e, 

 or "niggers," as they are called; the larvte of the 

 lace-wing or " golden eye," and the larvie of the 

 hover-flies, which, as their name implies, hover over 



' Discovery, February 1921. 



" See article on " Immunity andj Plant Diseases," Dis- 

 covery, June 1920, p. 197. 



flowers; all of which feed voraciously on "green fly " 

 or aphis. The hover-fly larva is a greasy-looking, 

 elongated maggot with tiny head and no legs, and it 

 has a very business-like way of picking up green fly. 

 sucking them dry, and casting away the skin in a very 

 short space of time. A few minutes' observation of 

 one of these will show what effective aids they are to 

 the grower. In .\merica special attention is paid to 

 the breeding of ladybird-beetles, some of which feed 

 on scale insects and mealy bug as well as on aphis, 

 and they are released where they will do the most 

 good. Yet other insects, even smaller, are parasites, 

 in or on the pests of plants, and these super-parasites, 

 as they are called, help to keep in check many pests. 

 To sum up, growers of all kinds of plants are nowa- 

 days finding it much easier and cheaper to prevent 

 pests by killing them in their early stages, when they 

 are vulnerable, than to attempt to combat them by 

 spraying when they have come to maturity and the 

 damage has been done. 



What is the Nature of 

 the Unconscious Mind? 



By Joan Corrie 



At this time, when the new psychology, or psycho- 

 analysis, as it is generally called, is not only in actual 

 use as a method of curing neurotic ailments, and a 

 system of re-education for people who, from whatever 

 cause, have failed to adapt themselves suitably to life ; 

 but also is made the subject of letters to newspapers, 

 sermons from the pulpit, and discussions at afternoon 

 tea, it may be of interest to try and examine in a simple 

 and non-technical manner how the new psychology 

 differs from the old, and what is the nature of the 

 material with which it works. 



Psycho-analysis differs from academic psychology 

 in two ver}' important particulars. First, it is individual 

 instead of being merely collective. We used to learn 

 how — all brains being made on the same pattern — 

 all men think and feel and act. Psycho-analysis lifts 

 the individual out of this generalisation and says to 

 him, " Though specifically human in type, and so 

 conforming to the laws which govern human thought, 

 feeling, and action, yet because this one particular 

 mind belongs to you, and not to A or B or C, therefore 

 it is unlike all other minds, and is as individual and 

 unique as your features, which yet as parts of a human 

 face arc possessed by everyone." 



In the second place, academic psychology is almost 



