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 \l and in width from 33 to 63 \l. An average 
of all measurements made from material collected in the United 
States was 38.7 by 85.1 \l, 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 p. These figures agree very well 
with those obtained by Bauer (3) in Europe, the 
dimensions given by him being 28 to 31 by 83 \l 
(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 FlG - 2.— Lateral view 
support in data later presented which show what U ring 95 by 40 n. 
appear to be consistent differences in the dimen- f a ™ era ~ lv inn da 
f± m drawing. X 190. 
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.) Midler, 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. 
LARVJE. 
Freshly hatched larva? 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 larva? 
are very delicate, frail, and weak, and ill adapted to withstand un- 
