The Shoot
Regularities may appear in the distribution of division planes only in the extreme tip region. Over the outer part of the apex, the cells often appear to lie in one to three layers, which constitute the tunica. Enclosed by the tunica lies a core of cells that exhibits no distinct layering; this zone is the corpus. The layers of the tunica normally contribute to the surface layers of the plant , and the corpus provides the deeper lying tissues. The tunica—corpus analysis emphasizes the orientation of division planes, but apices can be examined from other points of view—the sizes of cells, the degree of vacuolation, and the concentration of various cell constituents , especially ribonucleic acid RNA , vary through the apex and this sometimes results in more or less distinctive zones.
Both gymnosperm and angiosperm apices have been classified on the bases of such zonal patterns, but the validity of this approach, as well as its usefulness for understanding the function of the apex as a morphogenetic centre, has been questioned. Since , a theory of angiosperm apical zonation developed by French and Belgian botanists has been gaining support. In longitudinal section, the differences contribute to the patterns distinguishable in apices, some of which have been used as bases for structural classification.
The main contention of the Franco-Belgian school, however, is that the zonation represents a functional difference. The cells have a restricted metabolism concerned primarily in maintaining a low rate of increase in cell number, and they themselves, as well as their immediate derivatives, take no part in organogenesis or associated differentiation. The anneau initial , by contrast, is that part of the apex that produces the beginnings, or primordia, of lateral organs. Not only is the division rate higher, but the tissue as a whole is involved in metabolic syntheses that precede morphogenesis.
One difficulty in investigating the stem apex arises from the uncertainty about which aspects are important for the overall function: Still another complication results because the apex is in a state of constant change during the growth of the plant. A long-term developmental trend begins after the definition of the growing point in early embryogenesis and continues thereafter through juvenility and the period of vegetative growth into the reproductive phase.
Superimposed on this trend is a cyclical change reflecting the periodic generation of the primordia of leaves and lateral shoots in the region immediately under the apex. Leaves originate on the flanks of the shoot apex. A local concentration of cell divisions marks the very beginning of a leaf; these cells then enlarge so as to form a nipple-shaped structure called the leaf buttress.
The cells of the leaf buttress may be derived from the tunica alone or from both the tunica and the corpus. In the early growth of the leaf primordium, new cells are contributed mainly by meristematic activity at the pole directed away from the stem, so that the buttress extends in length. The subsequent distribution of growth varies among the different groups of vascular plants according to the shape of the mature leaf.
The Shoot™
In considering the angiosperms, a broad-leaved dicotyledon e. Apical growth dominates in the tobacco-leaf primordium until a height of about 0. Thereafter, the buttress becomes more and more flattened in the transverse plane by laterally oriented cell divisions and further expansion growth on either side.
The dividing zones are the marginal meristems, through the activity of which the leaf gains its laminate form.
BlocBoy JB Does The Shoot Dance With Flamenco Dancers In "Mamacita" Video
In each meristem the outer file of cells, or marginal initials, contributes the epidermal layers by continued division. The cells below, the submarginal initials, provide the tissue of the inner part of the leaf. Usually a certain number of cell layers is defined in the mesophyll the parenchyma between the epidermal layers of a foliage leaf. Cell division is not limited to the region of the marginal meristems but continues throughout the leaf in each of the layers, always in the same plane, until the final cell number is approached.
The rate then declines, ceasing in the different layers at different times. Divisions usually end first in the epidermis, then in the lower mesophyll layers of a leaf such as that of tobacco, and last in the main photosynthetic tissue, the palisade layer, just beneath the upper epidermis. The vascular pattern in a tobacco leaf is determined early in the development of the vessel primordium. A procambial strand is formed by the elongation of narrow axial cells, and this extends both toward the base and toward the apex, eventually linking with the procambium of the stem.
When the marginal meristems become active, the lateral veins of the leaf are initiated first, followed by the third and later order branchings that give the characteristic network of veins in the mature leaf. Although the differentiation of the cells of the vascular system begins at the base, the epidermal and mesophyll cells mature from the tip inward toward the stem. The palisade cells elongate in a plane at right angles to the epidermis; those of the lower mesophyll expand irregularly to give lobed forms.
The cells of the epidermis, shaped like irregular paving stones, continue to expand in the plane of the leaf after growth ceases in the mesophyll, so that the cells of the internal tissues are pulled apart to form the system of air spaces found in the mature leaf. Dicotyledonous leaves are folded in various ways in the bud, the patterns being determined by differential growth in the tissues of the upper and lower surfaces laminae of the young leaves.
Differential growth may cause the lamina either to roll or fold toward the leaf midrib or to fold near lateral veins, thus pleating the lamina. The folds in the bud are, of course, eliminated during the final phase of leaf expansion.
BlocBoy JB Does The Shoot Dance With Flamenco Dancers In "Mamacita" Video
In the development of the maize leaf, the primordium arises first as a prominence some distance below the apical dome. The zone of division and growth extends laterally around the apex so that a complete collar forms; then the margins overlap. Meanwhile the original tip zone continues to elongate, eventually surpassing the stem apex. Tip growth declines thereafter, and further increase in cell number results from meristematic activity at the base. The early development of the vascular system is unlike that in dicotyledons, for several parallel procambial strands, rather than a single midrib, are initiated.
The first of these grow toward the apex, but, as tip growth ceases, procambial strands form above and extend toward the base, passing through the node, or point of insertion of the leaf primordium, and into the stem below. As the leaf extends in length, the tissues begin to mature first at the tip, and a wave of differentiation passes down toward the base, where cell division and extension growth may continue long after the tip of the leaf is mature. Protection for this immature and succulent tissue of the leaf base is afforded by the sheaths of older leaves surrounding it.
A session typically lasts between 1 to 2 hours depending on whether you have a student or full shoot and it can include as many dress changes and breaks as required. Four changes of outfit is usually more than enough though. I work with loads of people who are having headshots done for the first time. I'll talk you through it and take extra care to make sure you are reassured and relaxed! Whatever works best for you.
If you feel more comfortable having someone there with you then that's fine. I recommend clothing or tops that are quite plain and don't distract the attention away from you.
Avoid loud patterns and logos. A grey coloured top often seems to work well for most people. Also if you have something that is similar to your eye colour then bring it along, it will help to make your eyes pop. If you have brown eyes, I appreciate you might not have a brown coloured top so grey or green usually works well. Simple layering can also work quite well. Be aware of how low the neck line on your top is, especially if you're wearing it underneath a jacket.
As it's only a head and shoulders image, it can sometimes look like you are wearing a jacket with nothing underneath if the neck line is very low! It might also be worth considering what job or roles you will be applying for or how you want to be represented. Most of all make sure you bring an item that is typically you and is something that you feel good in. I know that clothes can get creased en-route so I have a rail for you to hang up all your clothing and an iron is also available, if neccesary.
The Accidental Prime Minister is a political drama based on the book of the same name, written by Sanjay Baru, who served as the media advisor of Manmohan Singh from to Akshaye Khanna also stars in the movie and essays the role of Baru.
BlocBoy JB drops his newest video off "Simi."
Shares it on social media. It is already on tv now. Best option is to share it myself. So here it is. It is not easy to portray him.