40 BOOT-KNOT AND ITS CONTROL. 



to the disturbed and to a large extent interrupted water supply 

 and to the accumulation above the gall of food substances which 

 would normally pass on to the root tip. They accordingly are made 

 use of in the formation of lateral roots at that point. It is probably 

 not different in its nature from the adventitious root formation in cot- 

 ton and other plants just above the point of entry of the wilt fungus 

 ( Neocosmospora vasinfecta) * or, in fact, from that occurring when 

 the end of a root is cut off or mechanically injured. The shape 

 or size of the gall does not seem to depend upon the place the plant 

 occupies in the current schemes of classification. The statement 

 of Frank ^ that the galls of the dicotyledons are mostly of the round, 

 tuberlike type, with lateral rootlets, wliile those of the monocoty- 

 ledons are mostly spindle shaped, without lateral rootlets, is not 

 confirmed by the writer's observations. Galls of both types may 

 be found on the same plant (PI. Ill, figs. 1 and 2) and appear to 

 owe their differences to the number of nematodes entering at a given 

 point, to the age and rapidity of growth of the root, and perhaps to 

 other causes. On both the beet and the radish, as well as on many 

 other plants, both types of galls and all gradations between may be 

 found. Entrance to the plant by the larvae is not confined to root 

 tips or to passage from galls to the adjacent healthy tissues, although 

 these are the usual ways by wliich a nematode reaches the point 

 where it undergoes its subsequent development. Nematodes are 

 also able to bore from the outside directly into the tender tissues 

 of other parts of the roots, and even into stems. Thus, not only are 

 the roots of potatoes attacked but even the tubers, while some- 

 times the prostrate stems of tomato plants as well as those buried 

 beneath the ground in setting out the young plants are badly 

 knotted. Indeed, Senor Komulo Escobar, of the Mexican Ministry 

 of Agriculture, informs the writer by letter that in the State of Nuevo 

 Leon the roots, stems, leaves, and even fruits of the watermelon are 

 attacked when they are in contact with the ground. This is excep- 

 tional, however, and is possible only where the nematodes are very 

 abundant and when the surface of the soil is constantly moist, so 

 that they are in its uppermost layers. 



Through the kindness of Mr. W. K. Winterhalter, then consulting 

 agriculturist of the American Beet-Sugar Co., at Rocky Ford, Colo., 

 analyses were made of sugar beets badly affected with root-knot 

 and of healthy beets from the same field. Strange to say, in six 

 samples each of healthy and diseased beets the average sugar 

 content differed less than one-fifth of 1 per cent of the total weight 

 of the beet, while the percentage of purity was equally as close in 

 the two lots. In these points there also seems to be a marked dis- 



i Orton, 1902, p. 10, fig. 1. > Frank, 1885. 



217 



