The simulation of the soil conditions of fall and winter. Seeds are placed in a moist, sterile potting medium or sand, or kept in a cold dry place â€“ depending on the treatment strategy (see Appendix B).
Read the entry on pretreating seeds first. Ok. So the seed must first undergo a cold period (just above freezing at 35 or so degrees F) before germination can occur. Instead of waiting an entire season or year, hasten the process by chilling seeds in the refrigerator. To prevent seeds from sticking and to keep them evenly damp, pack them together with vermiculite or sphagnum moss. Place in an airtight container or bag. Do not remove until the appropriate time period has passed. Each variety of seed has its own requirements.
The process of preparing a tree seed for sowing by dispersing the seeds in sand and subjecting them to cold conditions, outdoors or artificially in a freezer or - refridgerator. This encourages germination.
A pregermination treatment used for overcoming dormancy in certain seeds; the treatment consists of placing seeds in a moist, well-aerated medium for a specified number of months, usually at 3-5°C but occasionally at 20-22°C.
The process of artificially breaking seed dormancy by placing them in layers of moisture-retaining media, under generally cool and moist conditions, for a period of time, so as to simulate winter conditions. Basically, you try to fool the seed into thinking it has endured a long, North Country winter when, in fact, it has just spent a couple of months in your fridge.
In horticulture, stratification is the process of pretreating seeds to simulate natural conditions that a seed must endure before germination. Many seed species have what is called an embryonic dormancy and generally speaking will not sprout until this dormancy is broken.
stratified sample is one divided into a number of smaller samples. For example, in a survey covering a city, a stratified sample would divide the city into a number of smaller areas or strata (of known population) and sample a specific number of households in each stratum.
Process in which units with similar characteristics are divided into groups called strata before the sampling process begins. Each unit is assigned to one and only one stratum based on prior knowledge about the unit. Separate samples are then selected within each stratum.
This term is used to describe the arrangement of a body of water into two or more layers of different densities. Water expands, as it is heated (see Thermal Expansion); therefore hot water has a lower density than cooler water. In a storage water heater the less dense hot water "floats" above the cold water. This is a very stable arrangement and very little mixing can occur without mechanical agitation.
The separation of a fluid into two or more layers of uniform, but different densities. surface waves â€“A wave traveling on the interface between the air and water, visible to us as changes in the free surface elevation. thermocline â€“The simplest definition is the area of maximum temperature change (gradient) in the water column. This definition can fail however depending on the vertical resolution of the temperature profile (the distance between samples). A better definition is the area of maximum temperature change over a length scale suitable for the layer depths (e.g. in Cayuga Lake gradients over a meter rather then a millimeter).
The construction of a random sample, for practical purposes, by identifying groups within the population that tend to be relatively uniform and including strata, or groups, of the sample in numbers that proportionally represent their membership in the entire population.
Horizontal layering of water in a lake caused by temperature-related differences in density. A thermally stratified lake is generally divided into the epilimnion (uppermost, warm, mixed layer), metalimnion (middle layer of rapid change in temperature and density) and hypolimnion (lowest, cool, least mixed layer).
A sampling technique in which sampling is done separately for separate parts of the population. Stratification is often used to ensure that one has an adequate number of sampling units with relatively rare characteristics (e.g., stratification may be done on race/ethnic status if one wishes to make comparisons among racial/ethnic groups).
the tendency of competing trees and shrubs in a developing stand to separate into different layers. The stratification of a stand can provide distinct niches for wildlife. See canopy, understory, and herbaceous vegetation.
A layered structure of sedimentary rocks in which the individual layers can be traced a considerable distance. The layers can be caused by many differences which include materials of different composition, color, grain size or orientation.
separation of a study cohort into subgroups or strata according to specific characteristics such as age, gender, etc., so that these differences which might affect the outcome of the study, can be taken into account.
The division of water in lakes and ponds into layers with different temperatures and oxygen content. Oxygen content declines with depth, while the uppermost layer is warmest in summer and coolest in winter.
(a) The operation of storing seeds in, and often in alternate layers with a moist medium such as sand or peat, in order to maintain viability or overcome dormancy Ecol.). The disposition of vegetation in superposed storeys Stat.). Subdivision of a population into strata or blocks or sampling unit as a preliminary to sampling. Each stratum should be more homogeneous in respect of the variable being measured than the population as a whole. ( BCFT.).
A system which structures unequal access of the society's members to opportunities, wealth, power. Caste and class are two ways societies can be stratified. In addition to class in our own society, gender and ethnicity are important means of stratification.
Distinct layers of water in a dam or weir pool, formed when there is little movement to cause intermixing-usually in summer when deeper layers of water become cold and deoxygenated. These changes may, in turn, induce other water quality changes.
The separation of a sample population into non-overlapping groups based on a habitat or population characteristic that can be divided into multiple levels. Groups are homogeneous within, but distinct from, other strata.
The layering of water due to differences in density. Water's greatest density occurs at 39 Deg.F (4 Deg.C). As water warms during the summer, it remains near the surface while colder water remains near the bottom. Wind mixing determines the thickness of the warm surface water layer (epilimnion), which usually extends to a depth of about 20 feet. The narrow transition zone between the epilimnion and cold bottom water (hypolimnion) is called the metalimnion or thermocline.
With time, the liquid portion of a battery (the electrolyte) will separate into layers. The sulfuric acid will go to the bottom, and the water to the top. If allowed to sit in this condition the battery will be ruined. Equalization will bubble and mix the electrolyte eliminating this problem.
Layers of deposits that provide archaeologists with one of the major tools or clues for interpreting archaeological sites (stratigraphy). Over time, debris and soil accumulate in layers. Color, texture, and contents may change with each layer. Archaeologists try to explain how each layer was added--if it occurred naturally, deliberately (garbage), or from the collapse of structures--and they record it in detailed drawings so others can follow.
In archaeology, especially in the course of excavation, stratification is a paramount and base concept. It is largely based on the Law of Superposition. When archaeological finds are below the surface of the ground (as is most commonly the case), the identification of the context of each find is vital to enable the archaeologist to draw conclusions about the site and the nature and date of its occupation.
Occurs in blended fuels that have a compatibility problem. It is usually experienced when paraffinic based oils are mixed with asphaltic based oils, causing asphaltenes to precipitate and settle to the bottom of the tank.
A condition where the concentration of acid is greater at the bottom of the battery than at the top. This condition is caused by undercharging, and if not corrected can cause premature failure of the battery. This condition can be prevented by periodic equalization.
Over time, electrolyte tends to separate. The electrolyte at the top of the battery becomes watery while it becomes more acidic at the bottom. This effect is corrosive to the plates. Equalization of flooded (or wet) batteries helps reduce stratification. Jump to Top
Change in water quality that occurs when river flow slows due to a dam and colder, oxygen-depleted water sinks to the bottom. If water released to produce electricity is from the lower levels, the oxygen-depleted water can change downstream habitat.
A term referring to the uneven heat distribution of most forced air systems. Hot air is blown around your living space creating pockets of warm, then colder air. Hot air also tends to collect near the ceiling where it is needed the least.
A way of ordering individual people within a social system. The different rungs of the ladder depend on, for example, income, education, work, or power. The term can also mean ranking anything on different levels, by group or category.
division into groups. Stratification may also refer to a process to control for differences in confounding variables, by making separate estimates for groups of individuals who have the same values for the confounding variable. ( Therapy)
Statistical tool based on showing data so that individual characteristics can be observed. The process of grouping data according to common characteristics so that these differences which might affect the outcome of the research can be taken into account.
A technique for organizing data to better understand the process producing the data and to identify potential improvement opportunities. Stratification groups individual numbers into meaningful categories or classifications according to some criterion such as time, location, type, source, reason, etc.
An effect that occurs when air containing smoke particles or gaseous combustion products is heated by smouldering or burning material and, becoming less dense than the surrounding cooler air, rises until it reaches a level at which there is no longer a difference in temperature between it and the surrounding air. Stratification can also be caused by forced ventilation.