Imágenes de páginas

903. T. anceps, Hook. Sp. Fil. 1. p. 135, t. 40 ?
904. Hymenophyllum sericeum, Swartz.
905. H. hirsutum, Swartz.
906. 907 & 908. Trichomanes pyxidiferum, L. var.

909. T. angustatum, Carm.; Hook. & Grev. Ic. Fil. t. 166; Hook. in . litt.

910. Metzgeria fucoides, Nees & Montagne.
911. Trichomanes membranaceum, L.
912 & 913. T. muscoides, Swartz.
914. T. apodum, Hook, & Grev. Ic. Fil. t. 117.
915. T. reptans, Swartz.
916. T. holopterum, Kunze, Fil. 1, p. 185, t. 77 ?
917. Hymenophyllum asplenoides, Swartz.
918. Hymenophyllum.
919. H. undulatum, Swartz.
920. H. abruptum, Hook. Sp. Fil. 1, p. 88, t. 31.
921. Gleichenia pubescens, Willd.
922. G. dichotoma, Willd.

923. Nephrodium Serra, Desv. Ann. Linn. 6, p. 253. (Aspidium Serra, Swartz.)

924. Danæa nodosa, Smith ; Hook. & Grev. Ic. Fil. t. 51. 925. Lygodium Poeppigianum, Presl. Suppl. Tent. p. 103? 926. Schizæa dichotoma, Swartz.

927. Rhipidopteris peltata, Fée. 2me. Mém. p. 78. (Acrostichum peltatum, Swartz.)

928. Anemia adiantifolia, Swartz.

929. A. Breuteliana, Presl. l. c. p. 90. (A. Mandioccana, Hook. Gen. Fil. t. 90.)

930. Ophioglossum vulgatum, L. (Ophioglossum reticulatum, L.)

Dr. J. D. Hooker in the Flora of New Zealand unites all the species of Ophioglossum proper, and Sir W. J. Hooker, in his and Dr. Arnott's Flora of Great Britain, says he is ready to acknowledge the correctness of this view.

931. Psilotum triquetrum, Swartz.
932. Lycopodium cernuum, L.
933. L. reflexum, Swartz ; Hook, in litt.
934. L. linifolium, L.
935. L. verticillatum, L.
937. L. taxifolium, Swartz.
938, 939 & 940. Species of Selaginella.

ART. XXIV.—Some observations on the Motions of certain Wind

ing Plants; by Wm. II. BREWER, Prof. of Chemistry in Washington College, Pa.

It has long been recognized as a general law, that green plants during their growth grow towards the light, but all the botanical works that have come under my observation, which speak of winding plants and tendrils in this connection, speak of them as forming, practically, an exception to this law, that is, that they turn towards some "dark" or "opaque" object. That they do turn towards a solid support has long been observed, the fact is undisputed, and the cause of this motion, instinctive as it were, towards some solid around which they may twine has always been given, directly or inferentially as the absence of light, or more properly the opacity or non-luminous character of the support. I have been unable to find any account of experiments on this property of certain plants or of certain organs of plants further than merely to show the fact that it exists.

During the summer of 1855 I made some observations on the growth of a hop vine (Humulus) to ascertain more precisely the relations between the rate of growth at different hours of the day, and the temperature, clearness and other atmospheric conditions. To effect this the vine was measured at stated hours several times each day, and the better to do this it was not allowed to wind around, but was trained up one side of a smooth pole. Incidental to the desired observations, it was noticed that during the heat of the day, although the plant sometimes grew several inches, it grew towards the light with only a very slight tendency to wind around the pole, while during the night, or on cold days, while the rate of growth was slower it would assume the spiral and cling closely to the support. On one occasion, when a number of plants were only from one to two feet high, a slight fall of snow took place which remained a day or more, and in a few hours, all the plants which had sprung up from the ground and remained perfectly erect until this time, inclined at a high angle towards a lattice which was artificially heated.

It was also found that they would climb a transparent glass tube almost or quite as readily as an opaque stick. These and similar observations at other times suggested to me that the cause of the motion towards a support was not owing to any influence of light, or its absence, but rather to heat, and to elucidate this subject a series of experiments were made at Ovid, N. Y., during the last summer.

These consisted in the main of presenting a warm and a cold support to some winding plant, and then observing if it manifested any preference. The plants experimented on were the

common Lima bean (Phaseolus lunatus L.) and the common morning glory, (Convolvulus purpureus L.) The general plan was to keep the plants in a closed room during the day and early part of the evening, where the air could be kept at a rather high and nearly constant temperature, and then remove them for the night into another room where the temperature was several degrees lower than the first, where the warm and cold supports were presented to them. This room was also closed and darkened that neither currents of air nor morning light should interfere with the accuracy of the experiments.

For the supports tin tubes were used, of the shape given in the figure, having a funnel a, at the top, and an elbow b, at the bottom, forming an obtuse angle. These were about an inch in diameter, similar in size and shape, and the vertical part painted black. These could be kept cool by filling with cold water, and if desired by placing ice in the funnel a, and could be warmed and kept at any desired temperature higher than the air, by a small spirit lamp placed under the end c. For the use of glass and other materials, an elbow of tin was employed, and then the straight tubes fitted with a cork. To test the effect of colors, tin tubes were painted of various colors, and in some cases colored paper was pasted around them. White, black, red, pink, green, blue, and yellow, were tried. When in use the tubes were

held in a nearly vertical position, about five 5 inches apart, one filled with well-water a few

degrees colder than the surrounding air, the other filled with warm water and kept heated to any desired temperature by a spirit lamp, generally from 5° to 12° Fahr., above the temperature of the air in the room. The plant was placed at the beginning of the experiment so as to be midway between the two tubes, not exactly parallel with them, but crossing their plane at a low angle. It was allowed to remain without disturbance from 9 P. M. until 7 A. M., and its position, the temperature of the air and the water in the tubes and other conditions accurately noted at the beginning and close of each experiment.

Many preliminary experiments were made to devise means to avoid the various causes of interference, and to test and perfect the apparatus, and they so far succeeded that I consider the results given as reliable. After these, a series of fifty-two experiments were carefully made, of which nineteen were with Convolvulus, and twenty-three with Phaseolus. These gave in thirty-six cases results confirmatory, that is, the vines turned to

or towards the warmed tube, in fourteen cases they showed no especial preference, and in only two cases did they turn to the cold tube. In these fifty-two experiments, the right tube was heated twenty-five times, and the results were nineteen confirmatory and six indifferent; the left tube twenty-seven times, and the results seventeen confirmatory, eight indifferent and two contradictory, (that is, turned to the cold tube). In both of these latter cases the nights were exceedingly hot (one was 84° F.) and the experiments were in a room in which the sun had shown a part of the day and the walls had become heated, so that on closing the room the temperature rose during the night several degrees; the heat radiated from the walls doubtless effected the results. During the cooler nights, or when the temperature was below 65° F., the results were most marked, and generally in the morning the point of the vine, left the evening before midway between the two tubes, would be found not only moved towards the heated tube but would be closely twining around it, the point of growth lying closely against the surface. The right and left tubes were in turn heated on alternate nights and also they were made to exchange places occasionally. As both of the plants experimented on wind to the left, (the right according to Bischof) it will be readily seen that it makes much difference which tube is heated, when the plant is placed in the position relative to them which I have described, in the form the spirals will assume. Thus, let a and b be the sections of the two tubes, and c the

extremity of the plant cd, at the beginning of the experiment. Then if a be heated (the one I have assumed as the left tube in the description) the plant will gradually assume the position of the dotted line mm, by simply turning to the left. If however, the right tube, b, be heated, the plant will take the direction of the dotted line nn, by first rising vertical and then passing behind and around the tube.

The room in which all the experiments

(with the tubes) were conducted had but one window, opening west, which at night was carefully closed and darkened. In half an hour, sometimes in a few minutes, after the light had been admitted in the morning, the growing point

of the vine would slightly relax the hold with which it would - press against the support, and then during the day its growth would be towards the light. During this period, the tendency to grow in the direction of the light was vastly greater towards the warmed tube; in fact, the Phaseolus seemed to be entirely insen. sible to the latter during this time, and the Convolvulus nearly so.


I found that the Phaseolus, if grown in a room in which the temperature was high and nearly constant, not falling more than 3° or 4° F. during the night, would wind about a support in such very long loose spirals that it could not retain its position, but would slide down from time to time, and this same plant, when allowed the influence of cooler nights, would then wind in shorter spirals and cling with its accustomed tenacity to the smooth stick which served as a support. Furthermore, I found that by placing a plant in such a position that the sun could shine on its growing extremity, but not on its support, and changing it occasionally to keep up the conditions, turning it so that its tendency to grow towards the light was in opposition to that of its winding, and then keeping it at night at nearly the same tem. perature that it had during the day, I could entice it entirely away from the support until a length of several feet of the vine was pendant and unsupported.

These indicate the same fact sustained by the experiments with the tubes, viz., that plants wind best when the support is warmer than the air. This condition is fulfilled in nature at night, as the solid absorbs the sun's rays by day and cools more slowly than the surrounding air by night. I am aware that such plants will wind in nature around cold supports, such as growing plants of other species, but I doubt if their first direction towards them, before the contact is more than accidental.

There appears to be much difference in the force with which different species of winding plants assume the spiral. The Con. volvulus seemed much more sensitive to the influence of heat than the Phaseolus, before it was in contact with anything, and much more independent of it afterward, for when once in contact with a support it could not be induced to again leave it, and would follow a piece of twine or slender rod apparently as readily as a more solid material. Many experiments seemed to indicate that contact with the support modifies the force with which plants assume the spiral, that in fact, although the fibres of the plant are somewhat spiral about its axis before contact, afterwards, these spirals are shorter, and only then will the whole plant assume a spiral form as if to enclose something in its turns.

This was beautifully shown by introducing the end of a vine into a thin glass tube at night; the fibres of the plant would assume a shorter spiral and sometimes the plant itself would wind around on the inner surface of the tube in the same form and direction as if it had enclosed some cylinder in its turns, while plants not so treated would remain nearly straight and their fibres less spiral.

The experiments with tubes of various colors gave no results materially different from the others.


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