PLANT DISEASES. 



741 



entrance into plants through wounds, it can readily be understood that 

 the act of pruning, unless the wounds made are promptly coated with 

 gas-tar, is very likely to be the means of admitting injurious fungi into 

 the living tissues of a tree. When pruning is done in late autumn or 

 winter there is no bleeding, the gas4ar is absorbed by the wood, and 

 infection prevented ; whereas when done in the spring bleeding takes 

 place, the saji oozes through the coating of tar, and fungus spores gain 

 an entrance. It is not an unusual thing to see fungi growing from a cut 

 surface that has been carefully protected by tar or other substance, but 

 pruned at the wrong time. 



Nowadays most people protect the cut surface of all branches of 

 more than one inch in diameter, leaving the hundreds of smaller cut 

 ends to take care of themselves. I am quite aware that it is not 

 practicable or even necessary to protect the ends of all cut twigs in the 

 case of a large tree. On the other hand, under certain conditions, it is 

 advisable to protect every cut surface. 



The accompanying figures illustrate sections of a portion of the stem 

 of two young standard Apple-trees. When the stocks were young all the 

 lateral branches were cut ofi', and not protected. The result was that a 

 parasitic fungus gained an entrance into the stem and spread upwards. 

 The fungus present in the tissues produced no immediate effect, and the 

 trees continued to grow for some years afterwards. When ten years old 

 a check in growth was experienced by the trees, and the fungus that had 

 been hitherto more or less latent became active, extended to the surface 

 of the stem, and during the same season the trees were killed, and in 

 addition bore a large quantity of microscopic fungi with mature spores 

 ready to be dispersed and attack other trees. The above is not an 

 isolated illustration ; hundreds of young trees perished in the same 

 nursery at the same time and from the same cause. 



It remains with the practical man to decide whether, under the 

 circumstances, it is not advisable to protect all cut surfaces, large and 

 small, on such an all-important factor as the stem of a young fruit-tree ; 

 for, although disease may not show itself for some years, it is perfectly 

 well known that many trees perish sooner or later from fungus infection 

 introduced into the trunk while quite young. 



VI.— General Summary of Leading Features Discussed in 



Previous Lectures. 



'I'he mode of life of many fungi is so very diflerent from that of flowering 

 plants that, unless the gardener is in possession of some of their pecu- 

 liarities, mistakes are certain to happen. As an illusti'ation, the bi-anches 

 of various kinds of Juniper are not unfre(|uently swollen, and covered 

 during the spring-time with soft, gelatinous, orange bodies of irregular 

 shape. These orange masses are clusters of spores, which produce other 

 still smaller spores that are blown about by wind, and such of those as 

 happen to alight on the surface of young damp leaves of the Hawthorn 

 or Pear germinate, enter the tissues of the leaf and cause a disease, result- 

 ing in the early fall of the foliage. Now if this epidemic is repeated for 



