THE ASCOSPORE AND OTHER FUNGI 257 



the Imperfect Fungi where the diseases discussed in the 

 last few pages are classified. The fungus causes strange 

 malformations of the roots of cabbage, cauliflower, and 

 other wild and cultivated members of the mustard famUy; 

 It reproduces by spores and is especially likely to. develop 

 in acid soils. Consequently liberal applications of lime 

 and rotation of crops are helpful methods of preventing in- 

 jury. Especial care should be taken not to throw diseased 

 roots upon the compost heap. It is better to burn them. 



OBSERVATIONS FOR PUPILS 

 Black Knot 



1. Is the Black Knot abundant in your locality ? Does it occur 

 upon wild cherry trees ? If so, upon what kind of wild chefrries is it 

 most abundant — the choke cherry, the wild black cherry, or the wild 

 red cherry ? 



2. Notice the difference between the dry or winter condition and 

 the velvety or summer condition of the knots. Feel the velvety coating. 



3. If a microscope is available, look at the spores from the velvety 

 surface by means of a high power. 



4. What preventive measures against Black Knot are used in your 

 locality ? Is there a law in your state requiring property owners to 

 destroy the knots ? 



5. Do you think that the presence of this disease along roads and 

 fences and in dooryards is a reflection upon the efficiency of your school 

 as an agent for the common good ? If so, why not organize a campaign 

 of extermination against the Black Knot ? 



6. Has one man a right to allow the spores of Black Knot to 

 develop on his trees to be blown to the trees of his neighbors ? 



7. Make a careful sketch of a twig, showing Black Knot, for your 

 booklet. 



Powdery Mildews 



1. Look at leaves of lilac, willow, and other plants to find those 

 affected by the whitish covering of the Powdery Mildews. 



2. Bring such leaves to school and study them as directed on pages 



