vinal] THE TEACHING OF PLANT DISEASES 305 



observing the color changes and decay effects without the use of a 

 microscope: Vegerables and fruits decay more readily in dark, 

 moist, warm cellars. Unclean receptacles aid decay. The skin 

 keeps out germs of decay. Decay is passed on by contact. Fruit 

 should be handled carefully. Coldness, dryness, and sunshine are 

 germ killers. 



Another series of experiments is with dishes of agar. Make 

 finger prints before and after washing the hands. Expose a dish 

 for five minutes before and for five minutes after sweeping ; before 

 and after a thunder shower; early in the morning and late in the 

 afternoon ; a drop of distilled water, faucet water, and dish water. 

 Try inoculation experiments with a sterile needle, as — removing 

 bits of decaying potatoes, oranges, onions, apples, parsnips, etc., to 

 a test tube with agar and stopping mouth of tube with absorbent 

 cotton. Inoculation now becomes a visible thing to the child. 



Visit a diseased potato field. Where is the disease thriving 

 most, — in the rich or poor soil, at the low moist end of the garden 

 or where it is well drained, where the foliage is crowded or where 

 plants are far apart, on the sunny corner or the shady corner? Are 

 there any varieties that appear to be more susceptible ? The class 

 will be impressed with the fact that the lack of proper food, over- 

 crowding, and absence of sunshine lowers the vitality of the plants 

 and makes them susceptible to disease. These conclusions must 

 make the conditions of human hygiene seem real and not a matter 

 of preaching. 



A field trip to a woodlot is also of great value. Find trees being 

 destroyed by fungi. What enabled the fungi to attack the tree? 

 See how many kinds can be collected. Find leaves with blemishes 

 and colored spots which are symptoms of disease. Symptoms in 

 plant diseases are much more evident than with people. 



A lesson on the higher parasites such as dodder, mistletoe, etc., 

 may be made a basis of morals. The law of the use and disuse of 

 parts is rather striking in these plants. 



A lesson in history will also be instructive such as a report on the 

 cause and effect of the potato blight in Ireland during the great 

 famine of 1844. 



Have an exhibition of moulds brought in from the homes. 

 Include everything, — shoes, books, fruits, preserves, etc. In class 

 discussion bring out the causes and emphasize the preventions. 

 Try to get an estimate as to how much is destroyed each year by 

 moulds in the home. 



