NEMATODE DISEASE OF WHEAT. 11 



symmetrical in shape. They are usually about twice as long as 

 broad, although individual eggs vary considerably in size even 

 within the same gall. This, however, is not surprising when it is 

 considered that these eggs in a gall may be laid by a number of 

 different females. In three lots of eggs obtained from mature galls 

 collected at widely separated points the writer noted a variation in 

 length from 73 to 140 y. and in width from 33 to 63 \i.. An average 

 of all measurements made from material collected in the United 

 States was 38.7 by 85.1 ^ while an equal number of observations taken 

 on eggs from a single lot of galls collected in China gave slightly 

 lower averages, namely, 37.1 by 71 \x. These figures agree very well 

 with those obtained by Bauer (3) in Europe, the 

 dimensions given by him being 28 to 31 by 83 ^ 

 (1/800 to 1/900 by 1/300 of an inch). Although 

 the different figures agree in general, there is yet 

 perhaps enough difference to warrant the sugges- 

 tion that definite strains of the nematode may 

 possibly occur. This suggestion finds further F * G - 2.— Lateral view 



. , , ,-..,. , of an old egg, meas- 



support in data later presented which show what ur i ng 95 by 40 /*. 

 appear to be consistent differences in the dimen- <£.a™in ra x i9o da 

 sions of larva? collected from various parts of the 

 world. Supporting evidence of possible strains of the organism is 

 also found in certain physiological variations. 



The eggs contain dense rounded granules, are semitransparent, and 

 possess a single central light spot, the nucleus. They are covered by 

 a tough, transparent, plastic coat or skin, probably chitinlike in 

 nature, but, unlike the eggs of another endoparasitic nematode, 

 Heterodera radicicola (Greef.) Miiller, they can not withstand 

 highly unfavorable conditions. This may be due to their not being 

 oviposited in a gelatinous protective secretion, as is the case with 

 the latter, and to their very rapid development. Just how long it 

 takes an egg to develop from the 1-celled state to an active larva 

 is not known. Segmentation, however, is rapid, probably requiring 

 not more than a few days at most, and it ordinarily takes place 

 after oviposition. Within a short time after the egg is deposited it 

 develops into an active larva which pierces the egg coat with its 

 anterior end, escapes, and leaves behind an empty transparent shell. 



LARV^. 



Freshly hatched larvae are transparent, threadlike animals usually 

 a little more than one-half millimeter in length. Such of their 

 organization as can be observed at low magnification is shown in 

 figure 3. In this first stage, which is of short duration, the larvae 

 are very delicate, frail, and weak, and ill adapted to withstand un- 



