September 21, 1917] 



SCIENCE 



281 



injured, many of them being in a dying condi- 

 tion. The bark was studded with the pustules 

 of the scab disease and abundant conidia were 

 present. Another collection was sent by Dr. 

 Henderson on request a" few weeks later. 

 Many of the twigs were now dead and few 

 conidia remained. 



Another collection of diseased twigs was re- 

 ceived about the first of April from Professor 

 Shaw, collected at Truro Agricultural College, 

 IST. S., also from a Mcintosh tree. Many of 

 these twigs were killed back several inches and 

 m the dead and also in the living bark abun- 

 dant pustules of the scab were present. The 

 affected twigs showed the characteristics de- 

 scribed by Morse and Darrows. The bark was 

 more or less thickly studded with light brown 

 spots which examination showed to be blister- 

 Uke areas due to the death and pushing out of 

 the epidermis of the twigs. Many of these 

 light-brown areas were roundish or oval with 

 a dark center. A number, however, lacked the 

 dark central area. Pieces of the diseased bark 

 were removed, embedded in paraffin and sec- 

 tioned, and the sections and diseased twigs ex- 

 amined. A well-developed stroma was present, 

 and many conidia beneath the raised epider- 

 mis. The dark center was composed chiefly of 

 the conidiophores of the fungus, the exposed 

 conidia having fallen away. 



Dr. Henderson and Professor Shaw were 

 asked to forward diseased twigs collected about 

 blossoming time, and both generously re- 

 sponded. The collection from Professor Shaw 

 was received about the first of June. A 

 few inches of the tips of some of these twigs 

 were dead, but the bark of the living parts and 

 of the living twigs contained many scattered 

 postules of the apple scab actively producing 

 conidia, the pustules being olive green from 

 the abimdant conidia. The dead parts of the 

 twigs were thickly covered with scab pustules 

 of the previous season, but the stroma was 

 dead or not producing conidia. 



The fresh conidia were placed in hanging 

 drops of distillated water and they germinated 

 as freely and vigorously as conidia obtained a 

 short time later from the young leaves of an 

 apple in the orchard. 



Pieces of the bark containing living pus- 

 tules were fixed, embedded in paraffin and sec- 

 tioned. The stroma was very well developed, 

 reaching a maximum thickness of 200 microns, 

 while the maximum thickness of the stroma on 

 the fruit was about 55 microns. It was also 

 evident that the stroma was actively produc- 

 ing conidia at the time of fixation. 



Mr. A. G. Turney^ describes the scab as 

 being troublesome in the twigs of susceptible 

 varieties and states that in one orchard all the 

 twigs of the previous year's growth of the 

 Fameuse were covered with scab spots. He 

 also found the amount of scab on the fruit was 

 much reduced by trimming off the diseased 

 twigs early in the spring. He had previously 

 failed to control scab in this orchard by spray- 

 ing alone. However, he does not claim the re- 

 sults were entirely due to the spraying. He 

 states in a letter to the writer that the scab is 

 quite common in the coastal regions as a twig 

 infestation, and it may be found also in al- 

 most any orchard inland, but rarely so bad as 

 to be a serious hindrance to growth. 



Professor Shaw in a letter to the writer 

 states that he found severe twig injury from 

 scab in several different regions in Nova 

 Scotia. The twigs collected at Mansonville, 

 Quebec, at blossoming time by Dr. Henderson 

 did not show any living pustules, but as not 

 many of them had been cut back into the living 

 wood the negative evidence was not satisfac- 

 tory. 



The twigs that had been received from 

 Truro, N. S., about the first of April were left 

 about eight weeks in the laboratory under ordi- 

 nary conditions. Conidia were then taken 

 from the scabbed areas and were tested in 

 hanging drops of distilled water for germina- 

 tion. A small percentage was found to germi- 

 nate. A second test gave the same result. The 

 spores were taken from beneath the blistered 

 bark, so that they had a certain amount of pro- 

 tection from the cold and from drying. 



The writer is convinced from these experi- 

 ments and observations that in certain regions 



3 Keport of the Horticulturist, Province of New 

 Brunswick, p. 100, 1915. 



