摘要:

Toxicity tests on four annual weeds,Thlaspi arvense L.;Brassica arvensis L. Ktze.;Chenopodium albumL.; andAvena fatuaL.; showed no definite evidence of a specific susceptibility of a given species to a given substance. The relative resistance of these four weeds to most substances, judging from the certainly lethal dose, was in the order 1:1:2:7. Of the 76 chemicals tested, the following most toxic compounds killed all four species at the dosages employed; selenic and chloric acids, sodium hydroxide, arsenic pentoxide, sodium arsenite, sodium and ammonium chlorate, ammonium thiocyanate, sodium cyanide, zinc chloride, sodium bichromate, sodium selenite, copper nitrate, sodium sulphide, formic acid, gasoline, phenol, creosote, tetralin, sodium benzoate, aniline, benzene and furfural. The residual toxic effect on the soil, three to four weeks after treatment, showed that of the 35 more toxic chemicals tested, only selenic acid and the five chlorates used had any appreciable effect at low and intermediate dosages, while eleven other substances depressed growth following the application of high dosages.

ISSN:1923-4287    

DOI:10.1139/cjr37c-024

出版商:NRC Research Press    

年代:1937

数据来源: NRC

摘要:

The relative importance of the different sources of canker varies from year to year. Some,e.g., pruning wounds and injuries from verticilliosis, become less, while others, such as dead twigs and fruit pedicels, become more significant with time. Still others show no definite trends but fluctuate according to conditions.Leaf scars are vulnerable for a time after leaf fall, because of a temporary absence of wound periderm in the leaf base, but the development of cankers from leaf scar infection is determined by an infrequent coincidence of physiological and meteorological factors.Some insects such as the oriental fruit moth (Laspeyresia molestaBusck.), the shot-hole borer (Scolytus rugulosusRatz.), and the peach borer (Synanthedon exitiosaSay.) can cause injuries which frequently become cankered afterwards. The lesser peach borer (Synanthedon pictipesG. & R.) is seldom a primary parasite but may stimulate necrotic processes through its destruction of callus in cankers. The peach is most susceptible to canker in the fall, and injuries such as pruning cuts made at that time are much more subject to infection than those made at any other time of the year. The incidence of peach canker and of winter injury can also be increased significantly by prolonging the period of open cultivation. At least three types of winter injury have been observed, all of which may give rise to serious cankers.From 75 to 85% of the open cankers of all ages overwintering on the tree remain active. There is also a tendency for cankers to become less active with increasing age. Surgical treatment of important cases is of considerable value.

ISSN:1923-4287    

DOI:10.1139/cjr37c-025

出版商:NRC Research Press    

年代:1937

数据来源: NRC

摘要:

Observations were made of the abundance ofBacterium globiformeConn in three soils that had been subjected to different fertilizer treatments. It was found that the organism was as numerous in a soil of low fertility which had been cropped continuously for 25 years without application of fertilizer as in plots of greater crop-producing power receiving farmyard manure and artificial fertilizer. Freezing of the soil under field and artificial conditions had no significant effect on the numbers of the organism.From the soils, 110 cultures ofBad.globiformewere isolated; ten strains were studied in detail. All showed characteristic metamorphosis from rod to coccus though variations in cell size and time-rates of change were observed. The change of shape is not merely a shortening of the rod until the organism becomes spherical, but involves a swelling of the rod followed by a fragmentation leaving ovoid bodies which become cocci.

ISSN:1923-4287    

DOI:10.1139/cjr37c-026

出版商:NRC Research Press    

年代:1937

数据来源: NRC