* 
88 MR. H. CHARLTON BASTIAN'S MONOGRAPH 
sprouting from the healthy seed, and then insert themselves between the sheaths of its 
leaves, gradually working their way round till they come 10 the innermost of these, Where 
they remain for a variable time, without increasing much in size, till the rudiment of the 
future ear begins to form. The length of time during which they remain in this situa. 
tion, and their degree of activity, depend upon the rapidity of growth of the plant 
and the moisture of the season. The remainder of the process may be best described in 
Davaine's own words; he says :—“ L’6pi du blé, avant de paraître au dehors, se forme 
et reste longtemps renfermé dans les gaines des dernières feuilles. Les anguillules, 
libres dans ces gaînes, le rencontrent et peuvent s'introduire entre les parties qui le 
composent. Pour que l'invasion des anguillules soit suivie de la production de la 
nielle, il faut que la rencontre ait lieu à une époque très-rapprochée de la formation de 
lépi. Lorsque celui-ci n'a encore que quelques millimétres de longueur, que les paléoles, 
les étamines et l'ovaire, ayant la forme d'écailles, ne sont point distincts les uns des 
autres, ces écailles sont constituées par des cellules naissantes très-molles, pulpeuses, qui 
se laissent pénétrer facilement, et c'est à cette époque que les anguillules en contact 
avec l'épi déterminent la production de la nielle, en s'introduisant dans leur parenchyme, 
Mais, lorsque ces écailles acquièrent la forme des diverses parties qui constituent la fleur 
du blé, lorsque le pistil bifide devient distinct, les anguillules ne pénètrent plus dans 
leur parenchyme, trop consistant sans doute, et la nielle ne peut plus être produite; 
c'est un fait que j'ai constaté par plusieurs expériences" (p. 18). This piercing and. 
occupation of a part of the rudimentary flower arrests its development, though it stimu- 
lates growth. A gall-like 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 twelve in each gall, and, 
after producing an enormous number of ova containing fully formed young—which 
speedily liberate themselves, though they afterwards undergo little change—themselves 
die and wither, at the time when the gall begins to assume its characteristie purplish- 
brown or black appearance. | 
In harmony with this method of infection of the wheat by the Vibrio tritici, as revealed 
by Davaine, I may state that in several grasses I have found different species of these 
free Nematodes, lying between the inner sheaths of the leaves, near the bottom of the 
culm. In Festuca elatior I met with no less than five species in this situation, belonging 
to the genera Dorylaimus, Mononchus, and Plectus; and in the stalks of wheat and oats 
removed from stubble-fields I have frequently found specimens either of these genera or 
of Rhabditis, Aphelenchus, or Cephalobus. In addition to a malady of oats and maize 
similar to that of the wheat, and said to be produced by the same animal, Steinbuch', 
nearly a century ago, recognized a disease somewhat similar to the “ purples” in two of the 
bent-grasses (Agrostis); and, from the frequent presence of these Nematoids in the situation 
named, I suspect such diseases of grass will be found more frequent, if specially looked 
cow A poo instance of disease induced in plants by these animals may be mn 
; "y of Kühn?, who has ascertained that a long-known and recognized 
disease of the common teasel (Dipsacus fullonum) is owing to the presence of a number 
* Naturforsch. xxviii 2 7, : 
ns S. 233, tab. v. * Zeitsch. für wissen. Zoolog. 1857, t. ix. p. 189- 
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