NEMATODE DISEASE OF WHEAT. 9 



because they are both caused by related species of nematodes. 

 Tulip-root is induced by another parasitic eelworm, the so-called 

 stem and bulb infesting nematode, Tylenchus dipsaci (Kuhn) Bas- 

 tian. This the writer has found in this country on hyacinths, 

 strawberries, clover, and other plants, but not on wheat. Ritzema 

 Bos (29), however, noted the disease on wheat, but described it 

 more in detail as it appears on oats. He notes that on wheat it 

 produces a swelling near the base of the plants, resulting in what 

 he calls a tulip-root appearance. He also states that definite dis- 

 colored areas result on the stems and leaves. The flowering parts, 

 however, usually are not attacked. As these two closely related 

 wheat diseases differ so strikingly in the way they affect the plant, 

 especially as the so-called "tulip-root" disease does not produce 

 flower galls and the other does, the two diseases are readily dis- 

 tinguishable. 



ORIGIN AND DESCRIPTION OF THE GALLS. 



The nematode galls may be short and thick or long and slender, 

 and in a dried condition they are nearly always smaller than the 

 wheat kernels. Dwarfed simple galls little more than the size of a 

 pinhead are sometimes found, while those nearly as large as wheat 

 grains are met with frequentty. Their size is mainly dependent 

 upon the number of larvae which enter them, as well as upon the 

 time when and place where the latter penetrate the tissues. 



Investigators differ as to the origin and nature of the tissue con- 

 stituting the flower gall. Davaine (11) thought that the larvae might 

 enter any portion of the flower and that, therefore, the composition 

 of the resulting gall merely depended upon what tissues were in- 

 vaded. Haberlandt (15) considered the galls to be largely, if not 

 entirely, of ovarian origin, while Prillieux (28) believed them 

 to be derived only from staminate tissue. Marcinowski (22), 

 after careful and constant macroscopic observations throughout 

 the development of the galls, concluded that they may arise (a) 

 from the undifferentiated flower bud, (b) at a later stage from 

 staminate tissues which are first differentiated, (c) from carpellate 

 tissues which are formed last, and (d) from tissue lying between the 

 stamens or between the carpels and stamens. Based on an examina- 

 tion of matured galls as they occur in the wheat spikes, the writer's 

 observations and interpretations agree in the main with those of 

 Marcinowski (22). 



Galls within the same flower may be simple; that is, may contain 



only a single cavity filled with the organism, as shown in Plate V, 



B, and in Plate VI, A, or they may be complex. The latter 



are composed of two or three of the single galls whose walls 



151572°— 20 2 



