38 KOOT-KNOT AND ITS CONTEOL. 



this unlikely since the larvae shun dry soil, and so would not be 

 present in that part of the soil which is dry enough to be transported 

 by the wind. More effective as means of transportation are the 

 hoofs of animals, wheels of vehicles, farm implements, and men's 

 boots. It is difficult to see how it would be possible to avoid conveying 

 living nematode larvae from one field to another on farm implements 

 if they are left, as is too often the case, uncleaned on being trans- 

 ferred from one field to the next. Thus, a wagon and horses going 

 from one field to another would, if the soil were at all damp, carry 

 some of the damp earth, probably containing nematode larvae, with 

 them. 



The foregoing explains the spread of nematodes after they have 

 once been introduced into a locahty. The introduction of nematodes 

 into a new locality, however, must have some other manner of accom- 

 plishment. This seems to be in most cases along with nursery stock. 

 Thus, the writer found that in parts of Texas the nematode appeared 

 first in the soil near fig and mulberry trees obtained from farther 

 east, which were noticed at the time of planting, several years ago, 

 to have knotted roots. In this way the soil near the trees became 

 infested and thence the disease spread, as previously described, to 

 different pomts in the locahty. Perhaps east of the irrigated districts 

 the fig, mulberry, and peach are responsible more than any other 

 plants for the spread of the disease. Since the putting into effect of 

 good nursery inspection much of this source of infection has been cut 

 off. In the u-rigated districts of Arizona and California the vme was 

 observed in several cases to be the plant at fault. The strawberry 

 has been observed at a few points in the East as the plant upon which 

 the pest was introduced. It is often badly affected without showing 

 much injury. A case has been called to the writer's attention in 

 which the disease was introduced into a garden in Washington, D, C, 

 by asparagus roots from an infested field. The wide distribution of 

 the disease in ginseng plantations is doubtless due to the setting out of 

 small rooted plants from infested regions, as well as to the practice 

 of some growers of packing the seed in damp earth. Should this 

 come, as is natural, from the vichiity of the ginseng bed and this 

 be affected by nematodes, the danger of sendmg nematodes along 

 with the seeds is very great. Tlie dirt used for packing is naturally 

 thrown out at the point where the seeds are planted, and thus the 

 larvae, if present, are able to enter the soil and infect the young gin- 

 seng seedlings. Seed potatoes are also another known source of 

 introduction of the disease.* In a personal communication Dr. N. A. 



1 Loiinshnry (1904) regards the potato as perhaps the chief source of introduction and spread of lliis dis- 

 ease in South Africa. 

 217 



