They are the most resistant to unfavourable conditions of environment, and are able, by a process of parthenogenesis, to give rise to ordinary, indifferent forms again, which can repopulate the gnat.
In 1953, he developed a method to make strains of wheat highly resistant to a single form of rust.
The substance is very resistant to the action of chemical reagents, to digestion, and possibly belongs to the glyco-proteids.
Owing to greater care on the part of growers, and the introduction of FrenchAmerican resistant stocks to replace vines attacked by the phylloxera, the wines in the early years of the 10th century again acquired a limited sale in England.
Cholera and typhoid organisms are less resistant, and are killed more quickly than tubercle bacilli at the above temperatures.
This lowland area, due to the non-resistant character of the strata,.
The belts of non-resistant rock have been worn away, leaving longitudinal valleys separated by hard rock ridges.
Calmette and Fraser found that when small doses of snake venom, insufficient to cause death, are injected into an animal, temporary disturbance is produced; but after a few days the animal recovers, and a larger dose is then required to produce any symptoms. By gradually increasing the dose the animal becomes more and more resistant, until at last a dose fifty times as great as that which would at first have produced immediate death can be injected without doing the animal any harm.
The highest points in the state are residual masses of relatively resistant rock rising above the erosion surface; such are: Rib Hill (1940 ft.) in Marathon county, in the north-central part, and some of the peaks of the Penokee Range in the N.
When the two lowlands are traced eastward they become confluent after the Niagara limestone has faded away in central New York, and the single lowland is continued under the name of Mohawk Valley, an east-west longitudinal depression that has been eroded on a belt of relatively weak strata between the resistant crystalline rocks of the Adirondacks on the north and the northern escarpment of the Appalachian plateau (Catskills-Helderbergs) on the south; forming a pathway of great historic and economic importance between the Atlantic seaports and the interior.
Trend to crustal deformations which in very early geological time gave a beginning to what later came to be the Appalachian mountain system; but this system had its climax of deformation so long ago (probably in Permian time) that it has since then been very generally reduced to moderate or low relief, and owes its present altitude either to renewed elevations along the earlier lines or to the survival of the most resistant rocks as residual mountains.
In certain parts of the plateau there are narrow anticlinal uplifts, an outlying effect of mountain-making compression; here a ridge rises if the exposed strata are resistant, as in Chestnut ridge of western Pennsylvania; but here a valley is excavated if the exposed strata are weak, as in Sequatchie Valley, a long narrow trough which cuts off a strip of the plateau from its greater body in Tennessee.
The surface is shown to be a plain of degradation by a gradual ascent here and there to the crest of a ragged escarpment, the cuesta-remnant of a resistant stratum; and by the presence of lava-capped mesas and dike-ridges, surmounting the general level by 500 ft.
New, disease resistant trees are bringing back the splendor of what has been called one of the prettiest towns in New England.
Special interest attaches to experiments made in the United States to endeavour to raise races of cotton resistant to the boll weevil.
Other woods, beautiful and precious, include guayacan (Guaiacum sanctum), baria (varia, Cordia gerascanthoides) - the fragrant, hard-wood Spanish elm - the quiebra-hacha (Copaifera hymenofolia), which three are of wonderful lasting qualities; the jiqui (Malpighia obovata), acana (Achras disecta, Bassia albescens), caigaran (or caguairan, Hymenaea floribunda), and the dagame (Calicophyllum candidissi- mum), which four, like the culla, are all wonderfully resistant to humidity; the caimatillo (Chrysophyllum oliviforme), the yaya (or yayajabico, yayabito: Erythalis fructicosa, Bocagea virgata, Guateria virgata, Asimina Blaini), a magnificent construction wood; the maboa (Cameraria latifolia) and the jocuma (jocum: Sideroxylon mastichodendron, Bumelia saticifolia), all of individual beauties and qualities.
In addition, the great majority have also another method of reproduction, for increasing the number of the parasites in any individual host; this is distinguished as multiplicative or endogenous reproduction, from the propagative or exogenous method (by means of the resistant spores), which serves for the infection of fresh hosts and secures the dissemination and survival of the species.
The height and massiveness of the mountains decrease to the south-west, where the piedmont belt sweeps westward around them in western Georgia and eastern Alabama Some of the residual mountains hereabouts are reduced to a mere skeleton or framework by the retrogressive penetration of widening valleys between wasting spurs; the very type of vanishing forms, Certain districts within the mountains, apparently consisting of less resistant crystalline rocks, have been reduced to basin-like peneplains in the same time that served only to grade the slopes and subdue the summits of the neighboring mountains of more resistant rocks; the best example of this kind is the Asheville peneplain in North Carolina, measuring about 40 by 20 m.
The feature referred to results from the occurrence here of a weak basal formation of clay overlaid by more resistant sandy strata; the clay belt has been stripped for a score or more of miles from its original inland overlap, and worn down in a longitudinal inner lowland, while the sandy belt retains a significant altitude of 200 or 300 ft.
The till is presumably made in part of preglacial soils, but it is more largely composed of rock waste mechanically comminuted by the crccpiiig ice sheets; although the crystalline rocks from Canada and some of the more resistant stratified rocks south of the Great Lakes occur as boulders and stones, a great part of the till has been crushed and ground to a clayey texture.
By a resistant Cretaceous limestone, which dips gently seaward; its scalloped inland-facing escarpment overlooks a denuded central prairie region of irregular structure and form; its gentle coastward slope (16 ft.
The results of the first cycle of erosion are seen in the widespread exposure of the resistant Carboniferous limestone as a broad platform in the south-western area of greater uplift through central Arizona, where the higher formations were worn away; and in the development of a series of huge, south-facing, retreating escarpments of irregular outline on the edges of the higher formations farther north.
Carbides of chromium are known; when the metal is heated in an electric furnace with excess of carbon, crystalline, C2Cr 3, is formed; this scratches quartz and topaz, and the crystals are very resistant to the action of acids; CCr 4 has also been described (H.
Turning now to instances of the opposite kind, it is known that silkworms which spin colourless cocoons are more resistant to the attacks of a certain deadly fungus than are those which spin the yellow ones.
Non-myelinate nerve fibres are as resistant to fatigue as are the myelinate.
The dove of thought falls lifeless if the resistant atmosphere of " the given " be withdrawn (Critique of Pure Reason, ed.
The bacillus is non-resistant and easily killed by heat and germicide substances, particularly acids.
Many remedies for this disease have been suggested, including total submersion of the vineyards, the use of carbon bisulphide for spraying, and of copper salts, but there appears to be little doubt that a really serious epidemic can only be dealt with by systematic destruction of the vines, followed by replanting with resistant varieties.
In spite of the many efforts in the direction of obtaining a resistant variety no great measure of success has been attained.
More remarkable still, animals inoculated with such " attenuated " bacilli proved to be curiously resistant to the deadly effects of subsequent inoculations of the non-attenuated form.
A The spores are capable of germination at once, or they may be kept for months and even years, and are very resistant against desiccation, heat and cold, &c. In a suitable medium and at a proper temperature the germination is completed in a few hours.