20 



Report on the Diseases of Wheat. 



When Needham placed this cottony mass in a drop of water, under 

 his microscope, he perceived to his surprise (as I did lately to mine, 

 before I was aware that the fact had been previously noticed) that 

 it was composed of a multitude of minute eel- shaped animalcules, 

 which were in active movement, twisting and wriggling to and 

 fro, like so many eels or snakes. The announcement of Need- 

 ham's discovery summoned several observers into the field, of 

 whom no one was more ])ersevering or intelligent than RoffVedi. 

 His papers, in the fifth and seventh volumes of the Journal de 

 Physique," contain the results of more than five years' patient 

 investigation into the economy of these minute creatures. In 

 the Philosophical Transactions" for the year 1823, Mr. Bauer 

 has also given the result of his personal observations and experi- 

 ments, carried through an equally long period, and without his 

 having any knowledge of what RofFredi or others had already 

 done so long before him. He has given faultless drawings of 

 the animalcule ( Vibrio tritici, as it is systematically named) from 

 the state of the egg to its full growth, and as it is seen under the 

 highest powers of the microscope. The disease which it occa- 

 sions is said to be sometimes very injurious to the wheat-crop ; 

 but I presume it must be very local, for it was unknown to some 

 of the earlier writers on the diseases of corn, who sought for it 

 without success ; and I could not learn, upon a limited enquiry, 

 that it was known to the farmers near Cambridge, or at Saffron 

 Walden. In this parish, however, it is well known, and my 

 miller informs me that he often has samples of wheat much in- 

 fested with it ; and among what he calls the tail- corn (the last 

 portions of a particular batch), he has found as much as half a 

 peck in the bushel. He says, also, that when the cottony mass 

 composed of the animalcules, is extracted from the grain in the 

 process of grinding, it does not pass through the cloth with the 

 fine flour in the beating, but remains behind with the bran. 

 When a sound grain of wheat is sown by the side of one infested 

 with the vibrio, the young plant which springs from the former is 

 not infected before March ; but then the animalcules begin to 

 find their way from the blighted grain into the earth, and thence 

 into the young corn. They gradually ascend within the stem till 

 they reach the ovule (or young state of the seed) in the flower- 

 bud, even before the ear has shown itself. Roffredi believed 

 that they do not increase in size till they have reached the young 

 seed, but that after this they grow very rapidly, soon deposit a 

 large number of eggs, and then die. Mr. Bauer has questioned 

 the accuracy of Roffredi's observation, and supposes the specimens 

 found in the stem to belong to another species. The young are 

 hatched in about eight or ten days after the eggs are laid, and 

 speedily attain to about the of an inch in length, and the tstV o 



