133 



of the stems they lost their property of avoiding the light. 

 The opposite direction during day and night was observed 

 previously by Bonnet. M. Dutrochet draws from these ob- 

 servations the following conclusions : 1. certain plants avoid 

 light, and this for the purpose of seizing hold of firm and 

 opake objects ; 2. the flexion of the stem towards the light, as 

 also from it, therefore in opposite directions, is the result of a 

 physiological action, and not of a superfluous elongation of 

 one side of the stem by which some botanists have endeavoured 

 to explain it. The roots exhibit no tendency either to grow 

 towards or from the light. 



In the explanation of the causes which give rise to the 

 windings and flexions of the stems of plants M. Dutrochet is 

 very complete, but he starts from points which are purely hy- 

 pothetical, and were demonstrated to be such in last year's 

 report. All flexions of plants are, as M. Dutrochet thinks 

 to have proved, produced by the action of two kinds of tissue, 

 which differ from each other both by their texture and the 

 principle of their action ; these two flexible tissues are the 

 cellular tissue and the fibrous tissue. The cellular tissue 

 bends by the action of endosmosis, and the fibrous tissue by 

 its filling with oxygen, &c. M. Dutrochet thinks that he has 

 observed that the inner cellular layer of the bark is in general 

 thickest in those plants which turn towards the light, and 

 considers the latter to be a natural consequence, that the cells 

 predominating in such bark and becoming smaller and smaller 

 from without inwards, swell by endosmosis. The contrary 

 appearance is said to be exhibited in such plants as turn 

 from the light : here for instance the cortical layer is said to 

 be the thickest. Starting from this notion, M. Dutrochet has 

 endeavoured to explain very completely all the difficult points 

 of this questionable subject, and a number of special observa- 

 tions are enumerated, which however collectively might easily 

 be refuted. 



M. Brunner* attempts to explain the winding of plants to 

 various sides from the different degree of irritability proper to 



them. Suppose a plant A. stand 



B. C, 

 A. 



at equal distance 



* Ganz anspruchsloser Versuch, das Links- und Rechts-winden der vor- 

 kommenden Pflanzen zu erklaren. Flora von 1837. No. 41. 



