TORSIONS. 



549 



torsions come into existence. A sufficiently clear idea of the matter may be 

 obtained by taking a straight piece of caoutchouc tubing or a leaden tube, and 

 fastening one end of it in some manner, while the other end is seized with the fingers 

 or a pair of tweezers and then twisted. By this means the superficial layers of the 

 body will be subjected to elongation, while its axis, or middle line, undergoes no 

 elongation at all, or if it is at the same time pulled in this direction, only a slight 

 one. It is obvious that something similar must occur by means of the processes of 

 growth during the torsion of the stem. 



Since then the internodes of a twining stem which are some distance from the 

 bud are made to undergo torsion by growth, the bud and the youngest internodes 

 which have not yet suffered torsion must be passively twisted or rotated around their 

 own axis — a movement which may easily be demonstrated by observing one of the 

 younger leaves from hour to hour : it is then seen that it is found first on the 

 upper side, then for example on the left flank, subsequently on the underside, and 

 finally on the right flank of the oblique or horizontal freely suspended tip of the shoot. 

 The torsions of twining plants must in some way be causally connected with their 

 very strong and long-continued growth in length ; since even in shoot-axes which 

 do not climb, and which in the normal condition are absolutely without torsion, it is 

 possible to produce torsions by intensifying the growth in length \ I pointed 

 out twenty years ago in this connection that the seedling stems of the Gourd, 

 Buckwheat, and other plants, when allowed to grow in profound darkness, where they 

 attain an enormous length, exhibit very evident torsions, and in consequence of the 

 movements connected with this occasionally become wound around neighbouring 

 objects of Hke kind, much as two twisted packthreads lying parallel and close 

 together spontaneously wrap themselves round one another. 



The question has often been raised whether any difference in the growth of the 

 plant by day and by night exists, and what it is. The question is in itself more of 

 practical than of theoretical interest. Its experimental treatment, which I accom- 

 plished in the years 1870-71, gave me an opportunity, however, of going more deeply 

 into the difficult problem of growth, since it was soon shown that this apparently so 

 simple question is only to be answered when all the external and internal factors of 

 growth are known and carefully balanced against one another ; and since my treatise 

 concerning the matter (' Üder defi Einfltiss der Lufttemperatur und des Tageslichtes auf 

 die stü7idliche)i und täglichen Änderungen des Längenwachsthums der hiternodien ') first 

 provided a firm basis for investigations in this direction, and has become the starting- 

 point of various investigations during the last ten years, it may be well to go some- 

 what more in detail into the contents of this treatise'^. 



' The influence,' I wrote, ' which the varying temperature of the air and the 

 periodic alternation of daylight and nocturnal darkness exert on the growth in length 

 of internodes and leaves after they have passed out of the bud-condition, has often 



^ I first described the torsions of the stems of etiolated seedlings mentioned in the text in my 

 treatise ' L/ier den Eitißuss des TageslicJits auf Neubildung und Entfaltung' (Bot. Zeit., 1S63, 2'» 

 Beilage, p. 16 — on p. 17, to the left, however, the words 'von Cucurbita'' should be added after 

 ' das hypocotyle Glied etiolirter Kci?npflanzen '). 



^ The general considerations on growth here given in abstract are contained in my treatise first 

 cited (cf. note i, p. 539). 



