Left Shape Research Articles

Spatial Memory Activity Distributions Indicate the Hippocampus Operates in a Continuous Manner.

There is a long-standing debate as to whether recollection is a continuous/graded process or a threshold/all-or-none process. In the current spatial memory functional magnetic resonance imaging (fMRI) study, we examined the hippocampal activity distributions—the magnitude of activity as a function of memory strength—to determine the nature of processing in this region. During encoding, participants viewed abstract shapes in the left or right visual field. During retrieval, old shapes were presented at fixation and participants classified each shape as previously in the “left” or “right” visual field followed by an “unsure”–“sure”–“very sure” confidence rating. The contrast of left-hits and left-misses produced two activations in the hippocampus. The hippocampal activity distributions for left shapes and right shapes were completely overlapping. Critically, the magnitude of activity associated with right-miss-very sure responses was significantly greater than zero. These results support the continuous model of recollection, which predicts overlapping activity distributions, and contradict the threshold model of recollection, which predicts a threshold above which only one distribution exists. Receiver operating characteristic analysis did not distinguish between models. The present results demonstrate that the hippocampus operates in a continuous manner during recollection and highlight the utility of analyzing activity distributions to determine the nature of neural processing.

Left-handed sperm removal by male Calopteryx damselflies (Odonata)

Male genitalia in several insect species are asymmetry in right and left shape. However, the function of such asymmetric male genitalia is still unclear. We found that the male genitalia of the damselfly Calopteryx cornelia (Odonata: Calopterygidae) are morphologically symmetric just after emergence but asymmetric after reproductive maturation. Males remove rival sperm stored in the female bursa copulatrix (single spherical sac) and the following spermatheca (Y-shaped tubular sac) prior to their own ejaculation to prevent sperm competition. Males possess the aedeagus with a recurved head to remove bursal sperm and a pair of spiny lateral processes to remove spermathecal sperm. The right lateral process is less developed than the left, and sperm stored in the right spermathecal tube are rarely removed. Experiments involving surgical cutting of each lateral process demonstrated that only the left process functions in spermathecal sperm removal. Thus, males of C. cornelia are left-handed in their sperm removal behaviour at copulation.

Cause Analysis of the Various Shapes of Leaves and Estimate the Actual Weight of the Leaves

The most attractive secret of the leaves is why they have the various shapes and the weight of the leaves. Based on the theory of gene and ecological environment, a model is built in this paper to explore it. The result can be extended to predict the weight of any parts of the tree and adapted for great majority kinds of trees.

Convective Cooling at Low Airspeeds and the Shapes of Broad Leaves

Circular, abstractly lobed, and leaf-shaped flat copper plates were heated in a very low-speed wind tunnel. Surface temperature distributions of the plates were matched to those of real leaves. With the centres of the plates 15 °C above ambient temperature, their heat dissipation was measured at wind velocities of < 1, 10, and 30 cm s_1 from below and laterally with horizontal and vertical plate orientations. Even very slight forced-air movements markedly increased heat dissipation in this range of mixed free and forced convection. Lobed plates were more effective dissipators than circles, with the greatest differences occurring where flow was normal to the plate. Circular plates dissipated about one-fourth more heat when vertical than when horizontal in still air (free convection). By contrast, dissipation was essen tially independent of orientation for extensively lobed models. Under some circumstances, maximum dissipation occurred with lobed plates oblique to a forced air stream. Physical explanations and biological implications of these results are discussed.

The Shapes of Leaves and Cotyledons

The Shapes of Leaves and Cotyledons

The Shapes of Leaves and Cotyledons

ATTEMPTS to explain the forms, colours, and other characteristics of animals and plants, though not new, were until recent years far from successful. Our Teutonic forefathers had a pretty story which explained certain characteristics of several common plants.

The Shapes of Leaves

MR. GRANT ALLEN'S papers in NATURE will evidently serve to direct attention to a most interesting subject which hitherto appears to have been much neglected. Every contribution of observed facts may tend to throw further light upon it, and I therefore venture to remark that one cause of the frequently filiform character of the leaves of water-plants appears to be the elongating action exercised upon the cells by the pressure of a rapid current of water, since it is obvious that growth must take place in the direction of the least resistance. With a radiate-veined leaf the tendency must be towards lateral pressure which would compress and elongate, and so give a linear form to the leaf-cells. I have been much interested to observe that on the seashore, in places where Fuci are exposed to this action by the ebbing tide, as when growing on the edge of a large boulder or hanging over its sides, the fronds and even the receptacles become unusually elongated. On the other hand, where a freshwater stream mingles with the salt water in pools left by the tide, and the endosmotic action of the water set up by its reduced density is greater, the algæ become broader if flat, or of more inflated character if tubular. This is well seen in Dumontia filiformis, Enteromorpha intestinalis, and Chondrus crispus. The influence exerted by the character of the surrounding medium and pressure may also be observed in that interesting genus of freshwater plants, Callitriche.

Mr. Grant Allen's Article on “The Shapes of Leaves”

THE article by Mr. Grant Allen on “The Shapes of Leaves,” published in NATURE (vol. xxvii. p. 439) as first of a series, calls for an emphatic protest on behalf of botanists, and especially of teachers of botany.

Mr. Grant Allen's Article on “The Shapes of Leaves”

As I do not think it necessary to preface four short papers on the shapes of leaves with a formal treatise on pbysiological botany, I am not careful to answer Mr. Bower in this matter. The word hydrocarbons was used deliberately, because the important point to notice is this—that the plant consists in the main of relatively deoxidised materials. From the point of view of energy, with which one has to deal mainly in treating of functious of leaves, that fact is of capital importance. I can conscientiously inform Mr. Bower that I was aware of the chemical constitution of proteids, and of the part which they bear in life generally; but I do not see what harm can be done to anybody by such a confessedly rough statement as that which he criticies. If we must always step aside to say all that we know about any subject whenever we have to deal with it, exposition of new matter becomes impossible. May I call Mr. Bower's attention to tbe further fact that in the same paper I spoke of the plant catching “fragments of carbon,” meaning thereby not free carbon, but carbon in the form of carbonic acid, even though it be merely reduced from carboa dioxide to carbon oxide. It seems to me that such roughly accurate language is permissible in popular writing, where one's main object is to insist only on the general principle involved. It is the carbon that the leaf wants, not the oxygen; it is the carbon and the hydrogen that it deals with, not the nitrogen, which is but the instrument for dealing with them; and the two other elements may therefore be safely neglected. Or must we drag in sulphur, and potassium, and calcium, and all the rest as well?

The Shapes of Leaves

The Shapes of Leaves

The Shapes of Leaves 1

The Shapes of Leaves 1

The Shapes of Leaves 1

IV.—Special Types in Special Environments FROM the previous papers it will be clear that degree of subordination to the stem accounts in large measure for the exteht to which leaves vary from the primitive ovate-lanceolate type. Where they are still so most subordinated, there will be a strong tendency towards the long pointed ribbon-like form, and also a marked inclination towards decurrence. This combination of peculiarities is well seen in several thistles, and in comfrey, as also to a less extent in many epilobes and stellarias. Compare Ver6ascum thaftsus, and other mulleins. From these extreme cases, in which leaf and stem are not fully differentiated from one another, one can trace several gradations, through square stems with sessile leaves (as in certain St. John's worts) up to merely sessile stem- leaves, or leaves that clasp the stem with pointed or rounded auricles. Wherever lines exist along the stem, they may be observed in pairs up to the point where a leaf is given off, and they are undoubtedly surviving marks of the primitive unity of stem and leaf. The same may be said of rows of hairs, like those of S/diana media and of Veronica charneedrys. There can be little doubt that special selective causes (protection against creeping;nsects, &c.) have often come into play in preserving or modifying such decurrent wings, stem-lines, auricles, clasping stipules, and rows of hairs; but as a whole they nevertheless point back distinctly to the origin of dicotyledonous stems from superposition of leaves and midribs upon one another. They are rudimentary forms of stemlamina.