July 28, 1905.] 



SCIENCE. 



121 



prune, poplar, quince, raspberry, rose, walnut 

 and willow. Of a number of these, little is 

 known of their nature. Those of the apple, 

 pear and quince are similar in nature, and are 

 not yet proven to be contagious. Those of 

 the almond, apricot, blackberry, cherry, peach, 

 plum, prune and possibly chestnut and walnut, 

 are similar in nature and origin, and are often 

 very contagious. Those of the grape and rose 

 appear to be slightly contagious, but can not 

 be classed with either of the preceding groups 

 with our present knowledge. The crown gall 

 or root galls of the hop contain a slime mold, 

 a Plasmodiophora resembling Plasmodiophora 

 trassicce. No study has been made at the 

 laboratory of the disease on the other plants 

 mentioned in the list, but these will be taken 

 up at once in connection with the others. 



Careful experiments with apple, quince and 

 pear seedlings raised from sterilized seed in 

 sterilized soil, watered with sterilized water, 

 indicate strongly that both the apple and pear 

 crown gall of the ordinary hard type, the one 

 devoid of numerous side roots or ' hairy roots,' 

 is not contagious. These seedlings of apple, 

 pear and quince inoculated with insertions of 

 live apple and pear galls beneath the bark and 

 wood of the roots, and also with minced galls 

 in the soil, remained free from disease in both 

 the control and inoculated portions of two 

 years' experiments. Carefully selected apple 

 seedlings grown in the nursery were inocu- 

 lated both in the greenhouse and in field plots. 

 In the experiments for two years the average 

 result from such inoculations was ten per cent, 

 of diseased plants in the inoculated portion 

 and fifteen per cent, in the control portions 

 of the plot. All galls were counted, whether 

 located on the plant at the place of inoculation 

 or not. Extensive inoculation of apple root 

 grafts in the field for two years gives an 

 average of 27 per cent, of plants with galls 

 both in inoculated and control portions of the 

 plots. About 10,000 apple trees were used in 

 the above sets of experiments. 



embodying a portion of the results of an investiga- 

 tion at the Mississippi Valley Laboratory of the 

 U. S. Department of Agriculture (Dr. Hermann 

 von Schrenk in charge ) . 



The ordinary apple crown gall is of two 

 types, the one a more or less woody gall with 

 no roots growing from it, the other with few 

 to numerous roots present. The former type 

 has been used in the experiments just de- 

 scribed. There is in addition a diseased form 

 called ' hairy root ' in which numerous side 

 roots branch from a stunted root. Galls may 

 or may not occur in connection with this 

 form, which is now considered a distinct dis- 

 ease, and which is at present under investiga- 

 tion. 



The crown galls of the peach, plum, cherry, 

 raspberry, almond and apricot have been 

 proved by careful inoculation experiments 

 with seedlings of each grown from sterilized 

 seed in sterilized soil, watered with sterilized 

 water, to be one and the same disease on each 

 of these plants. Peach and raspberry are 

 most susceptible to wound inoculation, but 

 also become diseased in infected soil without 

 artificial wounds being made. This disease 

 has not been contagious on the apple, pear 

 and quince. 



The results from an experiment with 300 

 two-year-old apple trees, 175 of which were 

 diseased and 125 healthy, all trees being se- 

 lected with care to have a uniformity of size 

 and root system, indicate that the disease has 

 no immediate effect on the duration of the 

 life of the tree where other diseases do not 

 enter. At the end of one year, five of the 

 healthy trees and seven of the diseased had 

 died, and no difference in the growth and 

 appearance of the two classes of trees could 

 be noted. This experiment will be continued 

 for' a number of years. Field observations 

 beaV out the conclusion that the disease does 

 not often kill young trees, as has been as- 

 serted. 



There is present on the roots of some apple 

 seedlings, and more rarely on grafted apple 

 trees a gall growth of a softer nature, more 

 like that on the stone fruits, and which may 

 prove to be of a slightly contagious nature. 

 A study is being made of this type and the 

 ' hairy root ' disease, which also occurs on the 

 cherry and peach. Grafted apple trees often 

 have as high as 50 per cent, of diseased trees, 

 budded trees, on the other hand, usually have 



