APPLE BLIGHT IN REVIEW. 21 5 



to investigate this matter of blight reported that in an old orchard 

 where the old trees had died out and every alternate row was planted 

 with young trees, that all of the old trees were affected wnth blight 

 while the young trees were not affected. 



Mr. Kellogg: Has electricity anything to do with it? 



Prof. Robertson : I could not tell you. 



Mr. Kellogg: It usually appears the strongest and seems to be 

 more prevalent immediately after a severe thunder storm. 



Air. Yahnke : That is natural when the atmosphere is full of 

 moisture which the leaves evaporate, and that is a favorable time for 

 growth of bacteria. 



Mr. H, H. Pond : Is there any known cause for the work stop- 

 ping unless it is on account of the winter coming on ? Sometimes a 

 limb will blight for a short distance, and then the work will stop. 



Prof. Robertson : I referred to that in my paper. Some men 

 have made investigations in the case of old wood, some in the soft 

 wood and some in the tips. In old wood it will simply make a spot, 

 so that in answer to this question I would say that it seems to me the 

 supply of food is not sufficient or the conditions are not favorable 

 for its further growth at that place, and after it has gone down the 

 branch a piece it stops. This twig blight you will find goes down 

 quite a distance sometimes and then stops. The amount of moisture, 

 condition of weather, temperature and so on we must always take 

 into consideration. We must also take into consideration the con- 

 dition of the tree and its ability to overcome those conditions which 

 may have something to do with it. They all stop in the fall w'hen 

 the amount of sap grows less. 



Mr. Brackett : We have heard a great many theories in regard 

 to blight, and a great many experimenters have come to the con- 

 clusion that after a while we could tell what kind of weather would 

 give us blight, and we would be able to tell the exact cause of blight. 

 I think until we know more about it the best thing we can do is to 

 plant our trees on a north slope where they do not get the hot sun. 

 Keep them in a good, healthy condition and do not let them over- 

 bear ; I believe that is one of the causes of blight. 



Mr. Bentz : You spoke of only one kind of blight. Is that all 

 there is? I find in my little orchard a blight on the bark and stock 

 of the tree. On the branches it spreads till it kills the tree. It starts 

 in a small spot. It came a year ago this last summer, and it has dis- 

 appeared but has left the marks of the former blight. Quite a 

 good many trees died of it, and a good many that w^ere affected 

 healed over this year. 



Prof. Robertson : If there w^as an injury in the old wood it may 

 have started there. Sometimes it may approach the tree by the 

 leaves dying above, but that is no sign if the leaves are affected, that 

 is no indication of the stem dying below. As Mr. Bentz says, this 

 injury will strike the stem, and you will not see the effects on the 

 bark for a long time, but it may gradually kill the tree. Sometimes 

 it stops right there and does not extend any further. 



Mr. Moore : That proves that the trunk should be protected ? 



Prof. Robertson : Yes, sir. 



