MECHANISM OF THE MOVEMENTS. 79/ 



present been too little investigated to allow of their being described here in a brief 

 space ^ 



(c) Closer attention has been paid to the phenomena connected with the stamens of 

 Cynaraceae^ Their external features in the normal condition have already been de- 

 scribed. For a close examination of them it is necessary to remove single flowers from 

 the capitiilum, and to cut away the corolla from below as far as the point of insertion of 

 the filaments, or to cut across the corolla-tube, stamens, and style above the insertion of 

 the filaments, and to fix the reproductive organs which are thus isolated by means of a 

 pin in damp air. When the filaments have recovered from the irritation caused by this 

 operation, they are convex outwards. The filanients are flat and strap-shaped ; they 

 consist of three or four layers of long cylindrical parenchymatous cells, separated by 

 thin straight septa, and surrounded by a layer of epidermal cells of similar form, 

 strongly cuticularised and growing out in many places to hairs, each of which is cut 

 off by a longitudinal wall. Unger states that intercellular spaces of considerable size lie 

 between the parenchymatous cells ; through the middle of the parenchyma passes a 

 delicate fibro-vascular bundle, which, like the epidermis^ is strongly stretched by the 

 turgid parenchyma. 



If the flower has been dissected according to the plan first described, and one of the 

 filaments, curved convexly outwards and fixed below to the corolla, above to the anther- 

 tube, is touched, it becomes straight and therefore shorter and in contact along its 

 whole length with the style. If all the filaments are touched, it is seen that they have 

 considerably decreased in length so as to draw down the anther-tube. After a few 

 minutes they resume their original length and curvature, and are then again irritable. 

 If the corolla has been dissected according to the second mode, where the filaments are 

 cut away and can move freely below, it is easily to see that every time they are touched 

 a curvature immediately ensues ; if the outer side is touched, it becomes at first concave, 

 then convex ; if the inner side is touched, it becomes concave, and sometimes after- 

 wards convex. The contraction of the irritated filament begins at the moment of con- 

 tact, after some time reaches its maximum, and the organ then at once begins again to 

 lengthen, at first quickly, then more slowly. The amount to which the irritated fila- 

 ments contract was determined by Colin from the mean of a number of measurements 

 in the case of Centaurea macrocephala and americana at i 2 p. c. of the maximum length ; 

 but he considers this estimate too low. Unger, whose measurements seem to be more 

 exact, gives the proportion at 26 p. c. ; he also observed that the filament does not 

 increase in thickness, while he gives the increase in breadth at 18 p. c. from the 

 original size ; and concludes from this (but incorrectly) that no decrease in mass results 

 from the irritation, but only a change in the shape of the filament. Pfeffer states in a 

 letter that the increase in thickness of the filament is much less than this, and not 

 nearly sufficient to prove that the irritation causes no decrease in mass. He supposes 



Blatter des sogenannten Sonnenthaues ; Bremen, 1782). That the movement is due to some other 

 cause than an irritability or contractility of the tissue is shown by the fact that the motion of the 

 glands is excited by living insects, or dead organic substances as raw meat, but not by inorganic 

 substances such as a piece of chalk. For further details see Gronland, Ann, des Sci, nat., 4th 

 series, vol. Ill, 1855, p. 297 ; Trecul, Ann. des Sci. nat. ditto, p. 303 ; A. W. Bennett in Quart, Journ. 

 Micr. Sci. 1873, p, 428 ; Mrs. Treat in Amer, Nat. December, 1873, p. 705 et seq.; Canby in Amer, 

 Nat. July, 1874, p. 396.— Ed.J 



^ See Unger, Anat, und Phys. p. 419. — Suringar, on Drosera, Vereeniging voor de Flora, van 

 Neederland eng. July 15, 1853, — Nitschke, on Drosera, Bot. Zeit. i860, No. 26 et seq. — Snetzler, on 

 Berberis, Bull, de la soc, Vaudoise des sci. nat, vol X, 1869. — Kabsch, on Berberis, Mimulus, &c., 

 Bot. Zeit. 1861, No. 4; on Stylidium, Bot. Zeit. 1861, No. 46. 



^ Cohn, Contractile Gewebe im Pflanzenreich, Breslau 1861 ; ditto, Zeitschrift fiir wiss. Zoologie, 

 vol, XII, Heft 3; Kabsch, Bot. Zeit, 1861, No. 4; Unger, Bot. Zeit. 1862, No. 15, and 1863, 

 No. 46, 



