14 SOME STEM TUMOES OR KNOTS ON APPLE AND QUINCE TREES. 



and of the trees with smooth roots about 32 per cent. This may be 

 accounted for in part by the increased tendency to throw out roots 

 in the case of the trees diseased with hairy-root. 



This peculiar behavior on the part of trees diseased with hairy- 

 root is further explained by another experiment. Since apple trees 

 are propagated commercially by grafting and budding, never by 

 cuttings, because they root so rarely, it was a surprise to find that 

 cuttings from trees with hairy-root are often able to throw out roots 

 readily. In an experiment where 100 cuttings were taken from the 

 shoots of yearling seedlings badly diseased wdth the simple form of 

 hairy-root (fig. 10) and planted in moist soil in the greenhouse in 

 earl}^ spring, more than 50 per cent rooted readily and 25 per cent 

 grew into trees. On the other hand, out of 100 cuttings taken from 

 healthy seedlings of the same lot, only 5 per cent rooted, and even 

 then so feebly that none of them grew into trees. This experiment 

 was carried out on an ordinary greenhouse bench with 8 inches of soil, 

 without bottom heat. 



Some of the diseased quince trees observed by the writer in Cali- 

 fornia Avere much stunted in their growth, but were considered a 

 profitable investment by the owner on account of the crops of fruit 

 which they had borne for several years. The quince trees in Cali- 

 fornia appear to be quite universally affected with this disease, 

 though usually with only a mild form. No indication has been found 

 that the disease spreads in the orchard from one tree to another, 

 either in the case of apple or quince trees, and experiments in which 

 inoculations were made with chips from living tumors indicate that 

 it is either very little or not at all contagious. In the case of apple 

 trees, the percentage of disease on the roots of trees in nursery rows 

 increases perceptibly from the first to the second year and remains 

 the same or decreases from the second to the third year. This observa- 

 tion is based upon an extensive experiment. 



It might easily be true that a reasonable amount of this disease 

 on a tree stimulates it and encourages fruit production. That it does 

 stimulate root production and may temporarily stimulate the growth 

 of the tree are facts now well known to the writer and have been ob- 

 served in many instances in the case of nursery trees. The disease, 

 therefore, appears to be not as injurious as one would think. It can 

 hardly be possible, however, that in the long run trees seriously 

 affected by this disease will not suffer. Branches badly affected, 

 as shown in figures 1 and 2, certainly must have their movement of 

 sap greatly impeded, their general activities much curtailed, and 

 eventually their life shortened. It is not believed, however, that small 

 tufts of hairy-roots on very limited areas of the root system of an 

 apple tree Avill in any way perceptibly affect the growth and fruit- 

 fulness of an apple tree or decrease its length of life. 



[Cir. 3] 



