LARCH DISEASE. 



43 



Y. Larch Disease — Investigation by the English Arhoricultural 



Society. 



In 1893 the English Arboricultural Society conducted an 

 inquiry into the disease of the larch by means of the circulation 

 oi a series of questions amongst its members. A report by 

 Dr Somerville on the results of the inquiry was published in 

 their Ti'ansactions for the year 1893-94, and a brief epitome of 

 this report will prove of interest to our readers at a time when 

 our own Society is about to investigate the same important 

 subject. 



1. Cause of the disease. The prevailing opinion was that frost, 

 either alone or in combination with other agencies, is the cause ; 

 but Dr Somerville says that the evidence of those who have 

 investigated the disease in a thoroughly scientific manner makes 

 it practically impossible to doubt that a parasitic fungus is the 

 primary cause, however much the latter may be assisted by 

 accessory circumstances. 



2. Is the disease less prevalent noxo than formerly ? Though the 

 larch may not be suffering quite so much in some districts as 

 formerly, the disease is, on the whole, as rampant as ever it was. 



3. Age at which trees are most liable to attack. The attack com- 

 mences during the early stages of growth, for the most part 

 between the seventh and the fifteenth years ; but the younger, 

 that is the upper and thin-barked, parts of the stems and 

 branches of old trees are equally liable to attack. Where the 

 stem is old, and consequently protected by thick bark, the fungus 

 has little chance of obtaining an entrance. The early attack is 

 far more serious in its effects than the later. 



4. Are the blisters more likely to occur at one fart of the stem 

 than at anotlier ? In a laige number of cases the disease appears 

 near the surface of the ground, also very frequently at the base 

 of a branch. The base of a tree is more continuously exposed to 

 the action of moisture than any other part of the stem. If rank 

 grass, ferns, or other plants cover the ground, they shelter the 

 stem near its base, and by interfering with the free circulation of 

 air, retard the evaporation of moisture. Water also rises from 

 the ground by capillary attraction, and becomes diffused over the 

 surface of the stem, and in these ways the conditions are rendered 

 favourable for the germination of fungus sj^ores. Wounds in 



