FREE NEMATOIDS. 
169 
ear begin to form. The length of time during which they 
remain in this situation, and their degree of activity, depend 
upon the rapidity of growth of the plant and the moisture of 
the season. It is well known that the rudiments of the ear are 
formed early, though this remains for a long time enclosed 
between the sheaths of the leaves before it makes its appearance 
externally ; and in order that this disease of the wheat may be 
produced, it is necessary that the young Nematoids should come 
into contact with the ear at a very early stage of its develop- 
ment, when the paleae, the stamens, and the ovary exist only as 
soft cellular scales, scarcely separated from one another. Whilst 
in this soft, almost pulpy condition, the several parts of the 
flower are easily penetrated by the young Nematoids, which 
would be quite unable to obtain an entry should they come 
into contact with the ear at a later stage of its development, 
when the several parts of the flower have become quite distinct 
from one another, and their tissue consolidated. This piercing 
and occupation of a part of the rudimentary flower arrests 
its development, though it stimulates growth. A galllike 
body is more rapidly produced in the site which should have 
been occupied by the germen, whilst the young worms soon 
become perfectly developed males and females. These vary in 
number from two to ten, or even twelve, in each gall, and in 
the course of time the females produce an enormous number of 
ova, each containing an embryo Nematoid coiled within, which 
soon liberates itself by bursting its membranous egg-shell, though 
it afterwards undergoes little change within the germen. The 
parent animals die, and their bodies shrivel, at the time when 
the gall begins to assume its characteristic purplish-brown or 
black appearance. When burst open, after soaking in water, 
it is found to contain myriads of the young animals with 
I remains of their membranous envelopes, together with the 
withered dead bodies of the parent Nematoids. In evidence 
! that the animals are not contained within an altered seed, as 
* formerly supposed, I may state that Davaine has occasionally 
■ found a small abortive germen within the same floral envelopes 
! with the gall, and in this case the gall has in all probability had 
; its origin in one of the rudimentary scales which would have 
gone to form a stamen. He believes it may be formed out of 
any of the scales belonging to the central parts of the flower ; 
and although, as a rule, all these parts participate in the forma- 
tion of a single central, still occasionally as many as three 
growths of this kind develop within the same pair of palece. 
On one occasion he found a growth of a similar nature and 
with the same kind of contents, growing from one of the leaves 
of the wheat. After this, additional proof as to the nature of 
the growth is almost superfluous. I may however add, that 
