Plants fall into four freeze-sensitivity categories: (1)tender; (2) slightly hardy; (3) moderately hardy; and (4) very hardy (Levitt,1980). Tender plants are those that have not developed avoidance ofintracellular freezing (e.g. mostly tropical plants). Slightly hardy plantsinclude most of the subtropical fruit trees, deciduous trees during certainperiods, and fruit and vegetable horticultural [truck] crops that are sensitiveto freezing down to about -5 °C. Moderately hardy plants include those thatcan accumulate sufficient solutes to resist freeze injury to temperatures as lowas -10 °C mainly by avoiding dehydration damage, but they are less able totolerate lower temperatures. Very hardy plants are able to avoid intracellularfreezing as well as avoid damage due to cell desiccation.
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Grapes and wine grapes are often damaged by spring-timefrosts. Since leaves form first, they are more prone to damage, but flowers andsmall berries are also sometimes damaged. Full recovery is common for leafdamage, but fruit damage can reduce production. The occurrence of early autumnfrosts increases susceptibility to fungi attacks (e.g. botrytis). During winter,dormant buds are very rarely damaged, since they can resist temperatures below-10 °C, down to -20 or even -30 °C (Leddet and Dereuddre, 1989). Table4.8 shows critical temperatures for grapes in relation to developmentalstage.
The 4-4-2 Formation - ThoughtCo
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Field experiments on critical damage temperatures for freshfruits and vegetable crops are somewhat limited, but the highest freezingtemperatures from studies on fruit and vegetable storage are provided in Table4.4. Although the critical damage temperatures might be slightly higher than theair temperatures at which damage is expected under field conditions, theinformation in Table 4.4 can be useful as a guide.
A guide to formations: The 4-4-2 • Outside of the Boot
In early and late winter and in early spring, plants may beless hardy, which enhances damage. Snow retention reduces this type of damage(Ventskevich, 1958). Later in the season, during flowering and initial graingrowth of cereals, frost damage reduces the number of kernels per spike. Thevisual result is that a bleached and thinner band forms on the spikes for eachfrost event, awns become curly, and because the weight of grain is less, spikesare upright near maturity (Figure 4.2).
How to play the 4-4-2 soccer formation with a diamond midfield
Although freeze sensitivity categories give generalinformation about the cold that a plant organ can endure before frost damageoccurs, hardening and phenological stage are almost as important. For example,temperature that produces both 10 percent ()and 90percent () bud kill increases as the season progresses fromfirst swelling to post bloom (Figure 4.1). In addition, the temperatures thatproduce bud kill in deciduous trees increases more rapidlyand approach the temperatures that produce kill.
System Of Play – the 4-4-2 Diamond Midfield
This formation, like others, tends to free up the full-backs, who will have more time on the ball than midfielders, particularly if the opposition is playing 4-4-2 as well.
Those talking about 4-4-2, often reducing the system to the Flat Four
Table 4.6 lists critical temperatures for almond treevarieties, where some of the data came from field observations usingtemperatures from standard shelters and some came from excised-branch climatechamber studies. In the table, the full-bloom data for cv. Peerless are somewhatdifferent for the field and chamber data, which illustrates the problem whencomparing chamber studies with field observations. According to Hansen'sfull-bloom data, 25 percent damage would be expected at -2.2 °C, whereasonly 1 percent damage was observed at -2.2 °C in the chamber studies. Ingeneral, for the same damage level, temperatures from chamber studies tend to belower than from field studies. Therefore, the critical damage temperatures inthe field are likely to be higher and damage could result when criticaltemperatures from chamber studies are used. If the bud, blossom or small-nuttemperatures were measured directly in the field rather than using sheltertemperatures, then the critical temperatures should be closer to those observedin the chamber studies. However, measuring bud, blossom or small-nuttemperatures is not simple. The main point is that published criticaltemperatures should not be viewed as absolutely correct, but only as a guidelinefor making decisions about when to start and stop active protectionmethods.