168 
POPULAK SCIENCE REVIEW. 
continue to move about for more than a week after such an 
occurrence. The tenacity of life of some of the species is most 
remarkable, and the young of the so-called Vibrio, or as I shall 
term it, Tylenchus tritici, afford the best known instance of this. 
But before speaking more in detail on this subject I am anxious 
to correct a very common misapprehension concerning the nature 
of the disease produced by this animal in wheat. 
This disease is generally very local, though persistent also in 
certain localities ; it is known to farmers under the name of 
Purples,” “ Pepper Corn,” or Ear Cockle.” Not to speak of 
the various accounts that have been given of the animal causiog it 
— which has been described as an ‘‘ infusorial animalcule,” and a 
‘‘ curious insect ” — it has been, and I believe still is, commonly 
believed that the hard purple or blackish bodies in which the 
animals are contained are the diseased seed of the wheat-ear. 
But Davaine has conclusively shown that the diseased product 
is not the altered seed, but is rather a species of gall ” or over- 
growth of natural tissue, produced by irritation, owing to the 
presence of the Nematoid — that it is, in fact,a production in every 
way analogous to the ordinary oak-gall. Eoffredi j and Bauer J 
were the only ones amongst the earlier observers who attempted 
to explain the precise way in which the young animals reached 
the ear: they both were of opinion that the young Nematoids 
obtained an entry into the vessels of the plant, whence they 
were carried onwards by the sap and so transmitted to the germen ; 
and in the opinion of this latter observer, the young animals 
found in this situation were the products of a second generation, 
whose parents had been produced by the original perforators 
within the vessels of the plant. 
According to the very accurate observations of Davaine, how- 
ever, which I am myself able to substantiate in great part, 
the method of production and 'nature of the disease is as follows 
When infected galls are sown with healthy seeds (or seeds are 
planted having young animals placed within their clefts), the 
young, in a week or so, according to the degree of moisture of 
the soil, make their way out of the softened gall, and, diffusing 
themselves in all directions, some come at last into contact with 
the budding plant just sprouting from the healthy seed. They 
then insinuate themselves between the sheaths of its leaves, 
gradually working their way around till they come to the 
innermost of these. Here they remain for a variable time, 
without increasing much in size, till the rudiments of the future 
* In an admirable memoir, entitled Recherches sur I’Angiiillule du Ble 
Nielle,” Paris, 1857. 
t Observ. sur la Physique, t. v. p. 1, 1775, 
t Philos. Trans. 1823, 
