326 ANNUAL OF SCIENTIFIC DISCOVERY. 



might be come to, that, although very large quantities of carbonic acid 

 were injurious to plants, yet that when present in water from one to 

 five per cent, it was beneficial. 



CAUSE OF THE POTATO DISEASE. 



THE precise causa of the potato disease is still unknown ; but we are 

 able at least to eliminate certain presumed causes, and to prove where 

 the disease begins, and how it reaches the tubers. It is pretty gener- 

 ally admitted at present, that the parts of the plant exposed to the air 

 are first attacked, and that their diseased state precedes that of the tu- 

 bers, and probably causes it. The following is a rather curious proof 

 that such is the case. M. Ghcldere, of Belgium, grafted some tobacco 

 plants upon potatoes. Success was probable, as the Nicotina and So- 

 lanum belong to the same family. The grafts did not merely take, a 

 fact of itself very interesting, but the plants happening to be in a field 

 of potatoes entirely attacked by the disease, the grafted stocks alone 

 remained exempt. If the tubers were sound in this case, it can only 

 be attributed to the presence of the leaves of tobacco not liable to the 

 disease, instead of the leaves of the potato itself. This fact is recorded 

 in the report on the exhibition of the products of Belgian agriculture 

 and horticulture. Bibliotheque Universelle, Feb. 



At a meeting of the Boston Society of Natural History in August, 

 Dr. Burnet called attention to a disease which had been noticed by 

 dealers, in the sweet potato. When the rot once became introduced 

 into a barrel of these potatoes, it would always go through the whole. 

 Examinations showed that this disease was a peculiar kind of fungus, 

 similar, though not identical, with that in the common potato. The 

 fact of its spreading through the barrel would argue that it was con- 

 tagious. Dr. Burnet did not attribute the disease to insects, but to 

 some chemical change in the cellular structure of the plant. 



PRESERVATION OF WHEAT FROM THE ATTACKS OF THE WEEVIL. 



NUMEROUS remedies have been proposed to protect wheat from the 

 destructive ravages of the weevil, but most of them have been im- 

 practicable or too expensive. M. Caillat, in the Comptes Rendus, rec- 

 ommends the use of tar as a certain and economical agent for their 

 destruction. He says, " the efficacy of tar in driving away the wee- 

 vil and preserving the grain is an incontestable fact. My father had, 

 a long time ago, his granaries, barns, and the whole house, infested 

 with these insects, so much so that they penetrated into all the chests, 

 and among the linen. He placed an open cask impregnated with tar 

 in the barn, and then in the granaries; at the end of some hours the 

 weevils were seen climbing along the walls by myriads, and flying in 

 all directions away from the cask. On moving this tarred vessel from 

 place to place, the premises were in a few days completely cleared of 

 these troublesome and pernicious guests. The agriculturalist who 

 wants to get rid of weevils, may, as soon as he perceives their pres- 

 ence, impregnate the surface of some old planks with tar, and place 



