Cambium

“ After the cambium has been active for some time producing secondary xylem and phloem, the latter consisting of sieve-tubes, phloem-parenchyma and frequently thick-walled fibres, a second cambium is developed in the pericycle; this produces a second vascular zone, which is in turn followed by a third cambium, and so on, until several hollow cylinders are developed. It has been recently shown that several cambium-zones may remain in a state of activity, so that the formation of a new cambium does not necessarily mark a cessation of growth in the more internal meristematic rings. ”

“ It is well known from studies of cambial growth that irregularities in the growth of the cambium are reflected in the irregularities in the shape and position of the wood fibers and vessels, which it forms. Ordinarily, if the cambium is wounded, the first cells formed are irregular in shape and orientation but after a wound is healed over the cambium cells resume their normal position. In parts of trees in which the grain is irregular or confused such as in the inner angle of crotches the shape of the cambium cells determines the nature of the grain beneath as shown in figure 3 (Ref. 1) . ”

“ The loss of limbs a tree can survive and start afresh. But girdle its trunk, exposing a ring of the cambium to the air, and the tree dies. The vital connection of leaves and roots is destroyed by the girdling; nothing can save the tree's life. Girdle a limb or a twig and all above the injury suffers practical amputation.
[Pg 22] The bark protects the cambium, and the cambium is the tissue which by cell multiplication in the growing season produces the yearly additions of wood and bark. Buds are growing points set along the twigs. They produce leafy shoots, as a rule. ”

“ But more have added a scarlet facing to their hunting coats, and some others are fairly aflame with the richest tint that any autumn leaf can get, the flaming crimson of the rock-maple foliage - 275 - ripened under a full sun where mountain brooks soak a primal vigor from the granite and send it upward into white cambium layers all summer long. ”

“ External to the sieve-tubes the tissue consists of radially arranged series of rectangular cells, some of which have already assumed the function of a cambium (c) . The tissue produced by the cambium on its inner edge consists of a varying amount of secondary xylem composed of very short spiral tracheids; a few of these may be lignified (fig. 133, A, x2) while others remain thin.
Phloem elements, recognisable by the presence of a thickened reticulum enclosing small sieve-areas (fig 133, B, s) are fairly abundant, and for the rest this intracambial region is composed of thin-walled parenchyma. ”

“ This layer, called the cambium, extends like a tight-fitting garment over the entire tree. Every tiny twig and spur is overlaid with it. If you ever had an "infected" finger from a scratch or pin prick or cut you have some idea of the danger the tree is exposed to when the cambium layer is laid bare and the wound neglected. Compare the two drawings on [442] this page. Look at the trees in your yard. Are there some like No. 1 and others like No. 2? In No. 1 the pruner cut a branch off close up to the main trunk. ”

“ Such meristematic layers are called secondary meristems. There are two chief secondary meristems, the cambium and the phellogen. The formation of secondary tissues is characteristic of most woody plants, to whatever class they belong. Every great group or phylum of vascular plants, when it has become dominant in the vegetation of the world, has produced members with the tree habit arising by the formation of a thick woody trunk, in most cases by the activity of a cambium. ”

“ In cases where the stock is of much slower growth than the graft, or the graft is inserted upon a stock of some other species, the descending cambium does not inclose the stock, but makes layers of wood on the stem of the graft, which thus, as is frequently seen, overgrows the stock, sometimes to such an extent as to make it unsightly. Nobody ever saw an apple shoot from a crab stock, a pear from a quince stock, or a peach shoot from a plum stock. This is one of the arguments in favor of the view that cambium also rises from the roots. ”

“ This new growth builds up from the cambium layer, which is the outside layer of wood cells that lies just beneath and in contact with the bark.
This is why it is so vitally necessary that the lines between the bark and cambium be placed in parallel contact as closely as possible, in the splice and cleft grafts. ”

“ Between them is a very delicate layer called cambium, which is [Pg 73] continually dividing and forming more wood on its inner side and more bast on its outer side. The wood is hard and resists pressure, while the bast is soft and is squeezed against the inside of the bark by the expanding wood (Fig. 43) .
The formation of new wood and bast takes place vigorously during the summer, at the expense of the food which is manufactured by the leaves and travels along the bast to the active cambium. As autumn comes, the activity of the tree slows down, and the new wood is formed of closer texture. ”

“ This cylinder of living cells, known as the cambium, extends between the wood and bark from one end of the tree to the other: by its periodic activity it adds new layers of tissue each year and thus, by increasing the amount of conducting tubes for the transport of water and for the distribution of elaborated food, it enables the tree to respond to the increasing demands which are the necessary accompaniment of increasing size. ”

“ The cambium cuts off externally a succession of segments which constitute additional cortical tissue (fig. 133, A, cr) of homogeneous structure, composed of parenchymatous cells containing starch and rich in intercellular spaces. As the stem grows in thickness the secondary cortex reaches a considerable breadth and the superficial layers are from time to time exfoliated as strips of dead and crushed tissue (fig. 133, A, b) . The diagrammatic sketch reproduced in fig. 133, A, serves to illustrate the arrangement and relative size of the tissue-regions65 in an Isoetes stem. ”

“ Sanio's treatise first removed this confusion of ideas, which appears in von Mohl himself to some extent even in 1858, by sharply distinguishing the thickening-ring beneath the point of the stem, in which the vascular bundles begin to be formed, from the true cambium, which is formed at a later time in and between the vascular bundles, and produces the secondary layers of wood and rind ”

“ Some are specialized to produce flowers and subsequently fruits. Leaves are extensions of cambium spread in the sun and air in the season when there is no danger from frosts. The leaves have been called the stomachs of a tree. They receive crude materials from the soil and the air and transmute them into starch under the action of sunlight. ”

“ Exposure to the air will kill it and completely destroy its functions in a few seconds. It is easily crushed by slight pressure and quickly killed by exposure to drying, frost, moisture and sunlight. Nature shows her extreme care of it for in making bark she has formed for the delicate cambium a perfect protective covering. Like the cambium the bark is composed of cells, as in fact are all animal and vegetable structures. But the cells of the bark have thick walls of a tough, corky substance, and each cell contains air instead of protoplasm. ”

“ C Calyx—The outer perianth or floral envelope, usually green in color; sepals, collectively. Cambium—A thin-walled formative tissue between the bark and wood. The active growing portion of the tree. Carpel—A simple pistil or one member of a compound pistil. Capsule—A dry fruit composed of more than one carpel and splitting open at maturity. Catkin—An ament or spike of unisexual flowers. Chambered—Said of the pith when interrupted by hollow spaces at rather regular intervals. Ciliate—Fringed with hairs on the margin. 148 Collateral—Accessory buds at the sides of auxiliary buds. ”

“ Inasmuch as the same cambium cells form fiber cells both on the inside to make the wood and towards the outside to make the bark, the direction and nature of the fibers in the bark are a direct indication of the direction of the fibers underneath the cambium in the wood. ”

“ In plants with a normal cambium the segments cut off from the initial layer fit on to the elements of the xylem or phloem to which they are to form additions, but in Lepidodendron it seems to be a general rule to find each of the most external lignified elements abutting on a group of two or three much smaller cells. It is difficult to believe that the meristem shown in fig. ”

“ In fact, a leaf is a layer of the precious cambium spread out on a framework of veins and covered [Pg 18] with a delicate, transparent skin—a sort of etherealized bark. What a vast quantity of leaf pulp is in the foliage of a large tree!
As summer wanes, and the upward tide of sap begins to fail, starch making in the leaf laboratories declines proportionately. Usually before midsummer the fresh green is dimmed. Dust and heat and insect injuries impair the leaf's capacity for work. The thrifty tree undertakes to withdraw the leaf pulp before winter comes. ”

“ The secondary xylem consists of radially disposed reticulate or scalariform tracheae, developed from a cambium-layer. The phloem is made up of thin-walled elements, including sieve-tubes and parenchyma. Both xylem and phloem include secondary medullary rays of parenchymatous cells. The cortex consists in part of fairly thick-walled elements; in older stems the greater part of the cortical region is cut off by the development of deep-seated layers of periderm. ”

“ In Shakespeare's day camomile grew in "the wild field by Richmond Green."
"Our ordinary Camomill [says Parkinson] is well known to all to have many small trailing branches set with very fine small leaves and spreading thick over the ground taking root as it spreadeth; the tops [Pg 246] of the branches have white flowers with yellow thrums in the middle, very like unto the Featherfew, but somewhat greater not so hard but more soft and gentle in handling and the whole herb is to be of a very sweet scent. ”

“ Common Pellitory is a very common plant, and will not be kept in our gardens without diligent looking to. The root goes down right into the ground bearing leaves, being long and finely cut upon the stalk, lying on the ground, much larger than the leaves of the Camomile are. At the top it bears one single large flower at a place, having a border of many leaves, white on the upper side, and reddish underneath, with a yellow thrum in the middle, not standing so close as that of Camomile. ”

“ The great series of Cambrian and pre-Cambrian strata in eastern North America from Alabama to Labrador; in western North America from Nevada and California far into Alberta and British Columbia, and also in China, [2] have been studied and searched for evidences of life until the conclusion has gradually been forced upon me that on the North American Continent we have no known pre-Cambrian marine deposits containing traces of organic remains, and that the abrupt appearance of the Cambrian fauna results from geological and not from biotic conditions. ”

“ Subsequent formations of Cambrian age came in a great group of alternating shale and sandstone followed by an immense thickness of limestone and shale. Fossils of Cambrian age, mainly Olenellus, are found as far down as the middle of the sandstone group. The strata lying beneath the fossiliferous beds differ in no material respect from those overlying. All are plainly due to the same causes and form part of one and the same group, and all are closely associated in area and structure. ”

“ When winds amidst the palms are sighing,
And fragrance breathes from every pine:4 [1]
When stars through cypress-boughs are gleaming,
And fire-flies wander bright and free,
Still of thy harps, thy mountains dreaming,
My thoughts, wild Cambria! dwell with thee! ”

“ The life of the Cambrian, though not so rich as in the succeeding Silurian period, nevertheless consists of representatives of most of the great classes of invertebrate animals. The coarse sandy deposits of the formation, which abound more particularly towards its lower part, naturally are to a large extent barren of fossils; but the muddy sediments, when not too highly cleaved, and especially towards the summit of the group, are replete with organic remains. ”

“ The traces of life in the Laurentian period, as we have seen, are but scanty; but the Cambrian Rocks—so called from their occurrence in North Wales and its borders ("Cambria ") —have yielded numerous remains of animals and some dubious plants. The Cambrian deposits have thus a special interest as being the oldest rocks in which occur any number of well-preserved and unquestionable organisms. We have here the remains of the first fauna, or assemblage of animals, of which we have at present knowledge. ”

“ During the Cambrian period the land subsided again, perhaps because of the weight of the uplifted sedimentary formations. During this subsidence the waters once again covered vast portions of North America, and additional muds and slimes were deposited on the bottom. It was at this period that life first appeared on the earth, in the form of simple marine organisms which have left fossil remains. These deposits made in the Cambrian period can be seen in outcroppings all through the region, although they are most notably found in the area about Deadwood. ”