Radicle

“ Whether or not a radicle, when surrounded by softened earth, is aided in forming a passage for itself by circumnutating, this movement can hardly fail to be of high importance, by guiding the radicle along a line of least resistance, as will be seen in the next chapter when we treat of the sensibility of the tip to contact. ”

“ There is another occasional movement which must not be passed over: the tip of the radicle, for a length of from 2 to 3 mm., was found in six instances, after an interval of about 24 or more hours, bent towards the bit of still attached card,—that is, in a direction exactly opposite to the previously induced curvature of the whole growing part for a length of from 7 to 8 mm. ”

“ Another seed was treated and observed in the same manner, but the radicle in this case protruded! inch, and was not fastened so as to project quite vertically upward. The filament was fixed close to its base. The tracing (Fig. 2, reduced one half) shows the movement
Fig. 2.—Brassica Oleracea: circumnutating and geotropic movement of radicle, traced on horizontal glass during forty-six hours. ”

“ The tip of the radicle, as soon as it protrudes from the seed-coats, begins to circumnutate, and the whole growing part continues to do so, probably for as long as growth continues. This movement of the radicle has been described in Brassica, Æsculus, Phaseolus, Vicia, Cucurbita, Quercus and Zea. ”

“ In a good part of the Radicle ’tis one entire Trunk; towards the Basis thereof, ’tis divided into three main Branches; the middlemost runneth directly into the Plume; the other two on either side it, after a little space, pass into the Lobes; where the said Branches dividing themselves into other smaller; and those into more, and smaller again, are terminated towards the Verges of each Lobe; in which manner the said inner Body being distributed, it becomes in each Lobe, a true and perfect Root. ”

“ Vicia faba.—Radicles of this plant were extended horizontally either over water or with their lower surfaces just touching it. Their tips had previously been cut off, in a direction as accurately transverse as could be done, to different lengths, measured from the apex of the root-cap, and which will be specified in each case. Light was always excluded. We had previously tried hundreds of unmutilated radicles under similar circumstances, and found that every one that was healthy became plainly geotropic in under 12 h. ”

“ We believe that there is no structure in plants more wonderful, as far as its functions are concerned, than the tip of the radicle. If the tip be lightly pressed or burned or cut, it transmits an influence to the upper adjoining part, causing it to bend away from the affected side ”

“ Radicles of Sinapis alba.—The radicles of some plants are indifferent, as far as curvature is concerned, to the action of light; whilst others bend towards and others from it. [6] Whether these movements are of any service to the plant is very doubtful, at least in the case of subterranean roots; they probably result from the radicles being sensitive to contact, moisture, and gravitation, and as a consequence to other irritants which are never naturally encountered. The radicles of Sinapis alba, when immersed in water and exposed to a lateral light, bend from it, or are apheliotropic. ”

“ The most important distinguishing characters of Connaraceæ consist in the insertion of the the two collateral ovula of each of its pistilla being near the base; while the radicle of the embryo is situated at the upper or opposite extremity of the seed, which is always solitary. In Connarus there is but one ovarium, and the seed (figured by Gærtner under the name of Omphalobium) is destitute of albumen. Rourea or Robergia has always five ovaria, though in general one only comes to maturity. Its seed, like that of Connarus, is without albumen, and the æstivation of the calyx is imbricate. ”

“ But the radii, from growing against rectangular indentations, or rather furrows, in the opposed compartments, come to be set a little inwards; and their external surfaces assume a very different appearance from the wall-portions of the compartments, which grow against the surface of attachment. In different species, the summits of the radii (and of the alæ) grow either very much more obliquely than in the species figured, or more squarely—that is, they extend from tip to tip of the adjoining compartments, parallel to the basis. ”

“ On the other hand, if the main body of the root points vertically down while the sensitive tip is horizontal, a curvature results, because as long as the tip is horizontal it is stimulated, and the stimulus is transmitted to the motor region.
This experiment proves not only that the tip of the root is the sense-organ for gravity, but also that the motile part is not directly sensitive; in other words, that gravitation is perceived exclusively in the tip of the root. ”

“ But no sooner are the marginal lines of her net firmly stretched, and two or three radii spun from its centre, than she continues her labor so quickly and unremittingly that the eye can scarcely follow her progress. The radii, to the number of about twenty, giving the net the appearance of a wheel, are speedily finished. She then proceeds to the centre, quickly turns herself round, and pulls each thread with her feet to ascertain its strength, breaking any one that seems defective and replacing it by another. ”

“ Commonly between the embracing spiral turnings or convolutions a great number of radial beams is developed, irregularly disposed and often branching; they support the thin spiral lamellæ and give to the whole shell more solidity. ”

“ Spongy framework of the solid sphere of the same structure throughout, with small, almost equal meshes, four to eight times as broad as the thin, elegantly denticulated bars; from the surface arise very numerous (two hundred to three hundred or more) curved, radial spines, as long as the radius, and of the same form as the bars. ”

“ If you imagine a cylindrical mass, with a cavity dug in the centre, whose edge conforms to the exterior edge; and if you place in this cavity another cylinder, higher than that which surrounds it, but so small as to leave between its sides and those of the cavity a hollow space, you will gain as distinct an image of this hill as words can convey. The summit of the inner rock was rugged, and covered with trees of unequal growth. ”

“ I allude to the discovery of radium by Madame Curie of Paris.
Radium has recently upset our most cherished theories of matter and force. The whole subject of chemistry has to be rewritten and our ideas of the constitution of matter entirely changed. Here is a substance which emits light and heat and electricity continuously without any apparent source of supply. It emits light in the dark, and in a cool room maintains itself constantly at a higher temperature than its environment. ”

“ Radii.—The radii are very wide in C. diadema. In all the species their summits are square or parallel to the basis. Their internal structure is remarkable: as the walls in this genus are extremely thin, so are the proper radii, for in fact they consist in this and all cases, as we know, of one margin of the wall modified by its lateral growth against the opposed compartment. ”

“ In the Articulates there is but one cavity, and the parts are here again arranged on either side of the longitudinal axis, but in these animals the whole body is divided from end to end into transverse rings or joints movable upon each other. In the Radiates we lose sight of the bilateral symmetry so prevalent in the other three, except as a very subordinate element of structure; the plan of this lowest type is an organic sphere, in which all parts bear definite relations to a vertical axis. ”

“ Radium covers an equal distance while we pronounce its name. One and one-quarter seconds, and twenty-five thousand miles are traversed. Puck promises to put his "girdle round the earth in forty minutes." Radium would pass the fairy girdlist in the spin round sixteen hundred times. Thus truth, as it is being evolved in our day, becomes stranger than the wildest imaginings of fiction. ”

“ Experiment 157.—I shall now describe the normal reaction of a growing organ to the unilateral stimulus of [Pg 413] thermal radiation. Figure 151 gives a record of response of the stem of Dregea to stimulus of short duration; the induced curvature is positive or towards the source of heat. On the cessation of stimulus, there is a recovery which is practically complete, and which takes place at a slower rate than the excitatory positive curvature. ”

“ In order, therefore, to find in what direction a ray of light will travel after striking a flat polished surface, we must draw a line at right angles to the surface at the point where the ray impinges on it, then the reflected ray will make an angle with the normal equal to that which the incident ray makes, or the angles of incidence and reflection will be equal. ”

“ For in a right sphere the needle is parallel to the plane of the horizon; but when the cœlestial pole is vertically overhead, or when the pole of the earth is itself the place of the region, then the needle is perpendicular to the horizon. ”

“ Radial Spines occur on the margin in the equatorial plane of the Discoidea in the greatest variety of number, form, size, and disposition. If the number be low (between two and eight) they are commonly regularly disposed; if the number be larger (ten to twenty or more) their disposition becomes commonly more or less irregular. The regular disposition is of great promorphological importance, as indicating the axes in which the growth is preponderant, and introduces other peculiar radial formations. ”

“ If the centre of the radiating lines is kept below the springing line, it adds greatly to the interest and beauty of the ornament. A succession of festoons or of drapery hanging from two points are examples of one species of curved radiation.{45}
Tangential Junction.—Euclid’s definition of a tangent is as follows:—“A straight line is said to touch a circle, when it meets the circle, and being produced does not cut it,” and is obtained by drawing a line perpendicular to any radius from the point at which it touches the circumference. ”

“ A ray cuts the surface generally in more than one point; hence it will happen that some of the rays touch the surface, if two of these points coincide. The points of contact of these rays will form some curve on the surface, and this will appear from the centre of projection as the boundary of the surface or of part of the surface. The outlines of all surfaces of solids which we see about us are formed by the points at which rays through our eye touch the surface. ”

“ Radial cells: the wing area between the radius and media; often divided: in the plural (Comst.) , are those cells anteriorly margined by the radius or its branches.
Radial cross vein: (Comst.) , is that which divides cell, radius 1.
Radial sector: in general, the lower of the two primary divisions of the radius (Comst.) : in Odonata, an indirect branch from the media, just below and parallel with media 2.
Radial vein: in Homoptera, the first important vein next the costa between it and ulnar: in Orthoptera, = radius (Comst.) : in Diptera, = 2d longitudinal vein (Meigen) , = radius 2 (Comst.) . ”

“ Moreover, if any transparent medium increases in density with depth, the amount of refraction will increase as the ray goes deeper, and the direction of the ray will be changed from a straight line into a curve, tending to become more and more perpendicular. ”

“ With the very weak radiation that I have used for my experiments, corresponding to the ordinary radiographic and radioscopic work, it has been easy for me to obtain images of metallic objects and human bones placed on a sensitive plate 15 feet from the radiating source, although the rays pass directly through a slab of marble an inch thick, a sheet of lead one-tenth of an inch thick, and a flooring eight inches deep, built of oak boards and rough plaster. ”

“ If the movement, though over a solid surface, is not constant in direction, but takes place as often on one side as on another, radial symmetry may be again looked for; and if the motions are still more variously directed—if they are not limited to approximately-plane surfaces, but extend to surfaces that are distributed all around with a regular irregularity—an approach of the radial towards the spherical symmetry is to be anticipated. ”

“ Arms at their distal end nearly as broad as long, and four times as broad as at their narrow base; their lateral edges concave, their terminal edge convex, without spines. Each arm is divided by seven to eight convex transverse septa into eight to nine simple, broad chambers. Central disk with three to four rings, about as broad as the fifth chamber. Patagium complete, connecting all the lateral edges of the arms.
Dimensions.—Radius of each arm 0.15, basal breadth 0.03, terminal breadth 0.12. ”

“ Radial contraction induces tangential stresses at the surface, colossal forces which bend over and invert the folds, and even thrust the strata one beneath another, causing them to be disposed like the tiles upon a roof. ”

“ Several have as their aim the study of the emanation, that strange gaseous body that radium produces and which is largely responsible for the intense radiation commonly attributed to the radium itself. Pierre Curie demonstrated by a searching examination the rigorous and invariable law according to which the emanation destroys itself, no matter what the conditions are in which it finds itself. To-day the emanation of radium, harvested in tiny phials, is commonly employed by physicians as a therapeutic agent. ”

“ The solid angle subtended at a given point by a closed curve is measured by the area of a spherical surface whose centre is the given point and whose radius is unity, the outline of which is traced by the intersection of the radius vector with the sphere as it traces the closed curve. ”