Principles of scientific botany, or, Botany as an inductive science / by J.M. Schleiden ; translated by Edwin Lankester.

Date:
1849
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Licence: Public Domain Mark

Credit: Principles of scientific botany, or, Botany as an inductive science / by J.M. Schleiden ; translated by Edwin Lankester. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    exception of the central rays) a refraction during their transit from the denser medium into the air, and this diverts them considerably from the rays of the axis; they strike, therefore, the periphery of the atmospheric globule, and on emerging from it again experience a refraction, by which they diverge so far from the rays of the axis, that they cannot arrive at the object-glass, and, consequently, not at the eye. A similar process takes place with all gases enclosed in a fluid. This, even at the present day, is a stumbling-block. We meet with elaborate explanations of a dark material said to be deposited in the membranous glands, and also with theories based upon the observation of them; but, on strict examination, we find that it is only the air enclosed in the stomates which has deluded the observer. Now we have plenty of means of convincing ourselves whether we have air before us or not ; for instance, water, which soon imbibes the air, caustic potash, alcohol, oil of turpentine, &c.; but we ought to expect from a practised observer that he should be able to distinguish air from a solid substance by merely looking at it. Air contained in the intercellular passages has also been described as a dark juice. On the other hand, air has been sought for where it can never be found. In man} works it is still stated that “ the epidermal cells contain air.” It only requires a glance through the microscope, and some elementary knowledge of optical science, to convince us that nothing more than fluid, which has nearly equally refractive power with water, is contained in the epidermal cells of any healthy living plant. But such matters are committed to paper, and copied again, without any one inquiring about their correctness or asking for reasons Drops of oil present the same appearance under the microscope, only with this difference, that the black margin in the oil-drops is much narrower, owing to the difference of refractive power between air and water being greater than between oil and water, and a greater number of rays are therefore lost in the air-bubble. The explanation is the same in tin's case as was given when speaking of the air, only the rays take exactly the opposite directions, owing to the greater refractive power of the oil. Other thick fluid substances, for instance mucus (protoplasma), assume different forms in fluids with which they are mixed, and in which they are not dissolved, and which forms are generally caused by their adhesion to other objects, as, for instance, to the surface on which they are examined, and in that case they are fibrous or membranous; ifj on the other hand, they are more iso- lated, and left to their own cohesive power, they assume a spherical form. B. There are also processes very generally met with which a microscopic observer ought to be acquainted with, in order not to be deceived by them when they occur. Certain motions, first of all, belong to such. a. Robert Brown, the gifted English botanist, first made the important dis- covery, that all substances, organic as well as inorganic, on being suspended in a fluid in sufficiently small particles, are in a state of constant trembling or vibratory motion, similar to a mass of monades, when seen with a low magnifying power. 1 he motion is difficult to be characterised, and it can only be accurately compre- hended, and distinguished from other similar motions, by frequent observation. It has been frequently observed in parts of plants, for instance, in the fine granular contents of the pollen-cells, and has been described as a special livinir action, which it certainly is not. We know nothing yet of the origin of these movements; but they are probably owing to slight electrical tensions and com- pensations. Another movement, which is frequently seen, is produced when two different jiids, w uch have a considerable affinity for each other, for instance, water and acoiol, or water and solution of iodine, are mixed with one another. A dh-ectionsCUUCn UbUa ^ ta^es ldace 1° them, frequently in quite opposite usu'dlv jK, ?i!L1S’ ThCn fluids rapidly evaporate. During this process there usuall) takes place a double current, namely, an upper one, from the margin to the centre of the drop, and a lower one, from the centre towards the margin. d. There are two further occurrences to be observed, which -five rise to fre- inTflu |US10,nS 5 °n,C ° .them 1S.the Process of solution. Since°most objects are objects^^takl nffi'ce 'm CrVatIOn * fre^nt]y happens that » solution of many objects takes place. The movements and changes of form occasioned thereby