INSECTS, DISEASES AND SPRAYING 59 



not reach the parts that are within the sub- 

 stance of the host. Such treatment, while 

 tending to check the spread by means of the 

 spores, will not be sufficient to arrest the 

 growth of the fungus that is already in the 

 tissue of the host. 



There is also a second form of spore that 

 is produced beneath the skin of the leaf and 

 out of reach of fungicides. As a precaution 

 it is therefore well to destroy any mildewed 

 leaves, or else when they fall the spores may 

 be set free. 



The Rose Rust (Phragmidium subcorticum, 

 Schr.) is a genuine rust similar to that of the 

 wheat, oats and other grains. It is not com- 

 mon upon indoor roses, but is sometimes and 

 in some places a troublesome pest upon roses 

 grown for ornament in the flower garden and 

 lawn. It attacks more especially hardy 

 hybrid varieties. All three forms of the fun- 

 gus are produced on the same host. The 

 aecidia appear in late spring on the leaves 

 and young shoots, forming powdery orange 

 patches, and often cause distortion of the 

 shoots. About midsummer the patches be- 

 come deeper in colour, owing to the formation 

 of uredospores. Finally the resting spores 



