A number of bundles were made up for them to carry.
They are disposed in two groups on either side, corresponding in the Polychaeta to the parapodia; the two bundles are commonly reduced among the earthworms to two pairs of setae or even to a single seta.
These bundles cotyledon.
The whole stele may be surrounded by a common external endodermis; sometimes there is an internal endodermis in addition, separating the bundles from the pith; while in other cases each bundle possesses a separate endodermis surrounding it.
At the nodes the relation of the endodermis to the bundles undergoes rather complex but definite changes.
One of them bundles says it's Mrs. Shipton's stuff but all it has in it is the white dress.
As the stele is traced farther upwards it becomes bulkier, as do the successive leaf-bundles which leave it.
Indications of polystely, frequent occurrence of extra-stelar concentric bundles, anomalous secondary thickening) which recall these complex types of stelar structure in the fossil Cycadofilices.
The vascular tissue is typically separable into distinct collateral bundles (figs.
These collateral bundles are separated from one another by bands of conjunctive tissues called primary medullary rays, which may be quite narrow or of considerable width.
When the pith is large celled, the xylems of the bundles are separated from it by a distinct layer of conjunctive tissue called the endocycle, and a similar layer, the pericycle, separates the phloem from the cortex.
The remaining bundles (compensation bundles) which go to make up the cylinder are such as have branched off from the leaf-traces, and will, after joining with others similarly given off, themselves form the traces of leaves situated at a higher level on the stem.
The leaf trace of any given leaf rarely consists of a single bundle only (unifascicular); the number of bundles of any given trace is always odd; they may either be situated all together before they leave the stele or they may be distributed at intervals round the stele.
The median bundles of the trace are typically the largest, and at any given level of the stem the bundles destined for the next leaf above are as a whole larger than the others which are destined to supply higher leaves.
Leaf-gaps are formed in essentially the same way as in the ferns, but when in the case of a plurifascicular trace the bundles are distributed at intervals round the cylinder it is obvious that several gaps must be formed as the different bundles leave the stele.
The gaps, are, however, often filled as they are formed by the development of external conjunctive tissue immediately above the points at which the bundles begin to bend out of the stele, so that sharply defined open gaps such as occur in fern-steles are but rarely met with in flowering plants.
The constitution of the stele of a flowering plant entirely from endarch collateral bundles, which are either themselves leaf-traces or will form leaf-traces after junction with other similar bundles, is the great characteristic of the stem-stele of flowering plants.
These collateral bundles are obviously highly individualized.
In some cases this individualization is carried ftirther, the cortex and pith becoming continuous between the bundles which appear as isolated strands em- Aberrant bedded in a general \, L.~/ ~ Typesof ground-tissue.
The bundles sometimes keep their arrangement s v in a ring corresponding with the stele, though the continuous cylin 0 der no longer exists (species of - Ranunculus).
In some astelic L- ~ stems (Nymphaeaceae) the number of bundles is greatly increased and they are scattered throughout the ground tissue.
A polystelic con g dition arises in some members of this order by the association of collateral 8 bundles round common centres.
It is possible to suppose that this condition is derived from the astelic condition already referred to, but the evidence on the whole leads to the conclusion that it has ansen byan increase in the number of the bundles within the stele, the individuality of the bundle asserting itself after its escape from the original bundle-ring of the primitive cylinder.
In the stems of many water-plants various stages of reduction of the vascular system, especially of the xylem, are met with, and very often this reduction leads to the formation of a compact stele in which the individuality of the separate Reduced bundles may be suppressed, so that a closed cylinder lmpbost~h1c of xylem surrounds a pith.
The leaf-bundles are always collateral (the phloem being turned downwards and the xylem upwards), even in Ferns, where the petiolar strands are concentric, and they have the ordinary mesodesm and peridesm of the collateral bundle.
The relation ~ of the laticiferous tissue to the assimi I lating cells under which they often end, and the fact that where this tissue is / richly developed the conducting paren ~ chyma of the bundles, and sometimes also 4 the sieve-tubes, are poorly developed, as well as various other facts, point to the conclusion that the laticiferous system has an important function in conducting plastic substances, in addition to acting as an excretory reservoir.
In this case also the differentiation of leaf-bundles, which typically begins at the base of the leaf and extends upwards into the leaf and downwards into the stem, is the first phenomenon in the development of vascular tissue, and is seen at a higher level than the formation of a stele.
The latter is produced (except in cases of complete astely where a cylinder is never formed) after a number of leaf-traces have appeared on different sides of the stem so as to form a circle as seen in transverse section, the spaces intervening between adjacent bundles becoming bridged by small-celled tissue closing the cylinder.
In this tissue fresh bundles may become differentiated, and what remains of it becomes the rays of the fully-formed stele.
This is especially the case in the young vascular bundles themselves (desmogen strands).
In the very frequent cases where the bundles have considerable individuality, the fibrous pericyclic cap very clearly has a common origin from the same strand of tissue as the vascular elements themselves.
It bears at its rim four bundles of very pronounced chaetae.
The connective tissue of the integument and basement membrane imperceptibly merges into that which surrounds the muscular bundles as they are united into denser and definite layers, and this is especially marked in those forms (Akrostomum) where the density of the muscular body-wall has considerably diminished, and the connective tissue has thus become much more prominent.
The small twigs, tied in bundles, are boiled for some time in water with broken biscuit or roasted grain; the resulting decoction is then poured into a cask with molasses or maple sugar and a little yeast, and left to ferment.
I, Interspaces between the muscular bundles of the root of the foot, causing the separate areae seen in fig.
(Lankester.) c, Muscular bundles forming the root of the foot, and adherent to the shell.
- The setae of the Polychaeta are disposed in two bundles in many genera, but in only one bundle in such forms as have no notopodium (e.g.
In these forms the bundles of setae are either capilliform or uncinate, and the dorsal setae of the thorax are like the ventral setae of the abdomen.
When present they are either arranged in four bundles of from one to ten or even more setae, or are disposed in continuous lines completely encircling each segment of the body.
Associated with these glands are frequently to be found bundles or pairs of long and variously modified setae which are termed penial setae,to distinguish them from other setae sometimes but not always associated with rather similarglandswhich are found anteriorly to these, and often in the immediate neighbourhood of the spermathecae; the latter are spoken of as genital setae.
On the other hand, in certain Polychaeta the bundles of setae are so extensive that they nearly form a complete circle surrounding the body; and in the Oligochaet genus Perichaeta (=Pheretima), and some allies, there is actually a complete circle of setae in each segment broken only by minute gaps, one dorsal, the other ventral.
The arrangement of the conducting tissue in the stem is characteristic; a transverse section of the very young stem shows a nunber of distinct conducting strands - vascular bundles - arranged in a ring round the pith; these soon become united to form a closed ring of bast and wood, separated by a layer of formative tissue (cambium).