A specialized conducting tissue of this kind, used mainly for transmitting organic substances, is always developed in plants where the region of assimilative activity is local in the plant-body, as it is in practically all the higher plants.
This is the case in the Fucaceae, and in a very marked degree in the Laminariaceae in question, where the assimilative frond is borne at the end of an extremely long supporting and conducting stipe.
Of supporting axes from assimilating appendages, and as the body increases in size and becomes a solid mass of cells or interwoven threads, a corresponding differentiation of a superficial assimilative system from the deep-lying parts.
The Marchantiaceae (see article BRYOPHYTA) show considerable tissue-differentiation, possessing a distinct assimilative system of cells, consisting of branched cell threads packed with chloroplasts and arising from the basal cells of large cavities in the upper part of the thallus.
The whole arrangement has a strong resemblance to the lacunae, mesophyll and stomata, which form the assimilative and transpiring (water-evaporating) apparatus in the leaves of flowering plants.
The midrib bears above a series of closely set, vertical, longitudinally-running plates of green assimilative cells over which the wings close in dry air so as to protect the assimilative and transpiring plates from excessive evaporation of water.
In the liverworts we find fixation of the thallus by water-absorbing rhizoids; in certain forms with a localized region of water-absorption the development of a primitive hydrom or water-conducting system; and in others with rather a massive type of thallus the differentiation of a special assimilative and transpiring system.
In the more highly developed series, the mosses, this last division of labor takes the form of the differentiation of special assimilative organs, the leaves, commonly with a midrib containing elongated cells for the ready removal of the products of assimilation; and in the typical forms with a localized absorptive region, a well-developed hydrom in the axis of the plant, as well as similar hydrom strands in the leaf-midribs, are constantly met with.
The root differs from the shoot in the characters of its surface tissues, in the absence of the green assimilative pigment chlorophyll, in the arrangement of its vascular system and in the mode of growth at the apex, all features which are in direct relation to its normally subterranean life and its fixative and absorptive functions.
Within the limits of the sporophyte generation the Pteridophytes and Phanerogams also differ from the Bryophytes in possessing special assimilative and transpiring organs, the leaves, though these organs are developed, as we have seen, in the gametophyte of many liverworts and of all the mosses.
Assimilative layer, and may also by the production of mucilage be of use in the protection of the body in various ways.
The cortex of a young stem is usually green, and plays a more or less important part in the assimilative function.
They appear to have been more ferocious and less assimilative than the other conquering tribes.
While conspicuously lacking in creative genius, the Ottomans have always shown themselves possessed of receptive and assimilative powers to a remarkable degree, the result being that the number of their writers both in prose and verse is enormous.
In philosophy there has been a remarkable increase of activity, partly assimilative or eclectic and partly original.
This assimilative policy attained its culminating point in the so-called decrees of rattachement (1881), in pursuance of which each ministerial department in France was made responsible for Algerine affairs which came by their nature within its jurisdiction.
When in the cell the assimilative processes exceed dissimilative, the external manifestations of energy are liable to cease or diminish.
The second factor inducing the assimilative change is the withdrawal of the nervous system from sensual, stimulation.
They lower the external activities of the cells, but do they not at the same time lower the internal, reparative, assimilative activity of the cell that in natural sleep goes vigorously forward preparing the system for the next day's drain on energy?