My dear Sir

That you value so highly the evidence I can give of the discoveries of Mr. Francis D., is the greatest honour I ever was treated with. When you believe my witness necessary for the establishment of truth before the scientific jury of your country, then of course I am willing to testify the matter of fact. It is not without timidity that I may produce my evidence before the public being well conscious of the incorrectness of my English; but if you will kindly put right my letter which was written without regard of publicity, the readers of “Nature” I hope will not be offended.²

I was not unacquainted with the paper of my friend Professor Hoffmann, concerning the contractile filaments he saw upon the annulus of Amanita muscaria, and I had myself in view to draw your attention upon those observations; but his statements, for ought I know, never having been confirmed by another author, I left; now of course Hoffmanns researches must be taken up anew.³

The day after I had sent my letter to you, I had the happiness to witness the contraction of a big filament protruded from the summit of a gland in a section which I had made the day before and kept under the coverglass in water in a wet chamber. The filament had got a length at least ten times the diameter of the glands throughout of the same thickness and of high refrangibility, its substance very soft, being shaked and moved by the least touch of the cover glass, even by the concussion of my breath. Adding a drop of distilled water to the section, I saw at once the filament bend undulatory and contract within a few seconds into a globulous, large mass on the top of the gland. Perhaps it was some extract out of the leaf-section, which by the added drop of water was floated towards the gland and filament, and caused the contraction of the latter. The protoplasm in the cells of this gland was rather pellucid and, homogene, while in glands without protruded filaments generally it seems opaque and cloudy; the summit of the gland being bent upwards, showed only four cells in cruciate juxtapposition (because the tertiary division of the apical cell which produces the eight cells of the gland, very commonly takes place in rather irregular way.)

The four crosswise cells showed each near the crossing point a small circular spot amidst the denser protoplasm of much less refrangibility, exactly as if there were a porus or hole in the cellwall; the filament itself arose from one of the marginal cells in which similar thinned spots were also visible.

The globulous masses which are very commonly found on the apex of the glands, are of very refringent matter, if freshly produced out of contracted filaments; but if kept several hours in water, they get much less dense and refracting, very like to common water, or spumous, like to soap-bubbles. Perhaps something of their substance is slowly dissolved in water.

A very curious fact I discovered several times, by adding Iodine to the detached epidermis of the leaf cups of Dipsacus; but it takes place only under conditions which I have not yet made out. The whole fluid-content of the cells of the epidermis got blue like diluted starch-paste, but no starch-granules are met in any epidermis-cell, with the only exception of the Stomatia;⁴*) the cell-walls and nuclei of course become yellow by Iodine. The basal-cell of the glands gets also blue by Iodine, the cells of the stalk yellow, the top of the gland brownish; the excreted globules become also yellow.

The cell-walls of the glands immediately under the cuticule consist of a substance capable of very much swelling; under certain circumstances those layers swell in water so much that the cell-contents appear like irregular globules amidst a gelatinous envelop. The same takes place with the club like hair’s composed of 4 cell-rows.

Having applied my studies mostly to the changes and movements of the protusions from the living glands in water, I have not been able hitherto to examine with sufficient exactness their chemical properties and behaviour to reagents which alone can give evidence of their true nature and composition.

But if I did remark in my last letter that there is no known analogy in plants of protoplasmatic, living protuberances protruded from gland-cells after the manner of pseudopopodia, I ought to aknowledge that we also do not know any case of mere secretion which behaves like the filaments of Dipsacus, and that this matter of fact stands hitherto single in biology—putting aside the observations of Hoffmann which want new confirmation.

The glands of Dipsacus are extremely sensible to the least hurt; they get spoiled and shrivelled in very short time in cut twigs; perhaps in a wetter season they are more enduring; but now the materials for farther researches begin to disappear; and I am obliged to interrupt my observations for some time which I intend to spend in a journey to Tyrol.

If you believe that one or another of these supplementary observations may happen to suit for publication in accession of the remarks of my last letter which you kindly wish to make known in “Nature” I leave them with pleasure to your disposition.⁵

As soon as I shall be able to come back to this highly interesting subject and to fill the lacunes of the present preliminary inquiry, I shall endeavour to publish a more detailed report in a German journal in agreement of the wishes you kindly made known to me.⁶

With the kindest regards and respects I remain | yours my dear Sir | very sincerely | Ferdinand Cohn

* Blue coloration of the content of the cells of the epidermis by Iodine has been ascertained in the leaves of Ornithogalum; but their chemical nature is not yet made out.⁷