dutrochet's experiments. 



205 



the stems which had a tendency to a perpendicular direction, but that 

 all the moveable parts of the plant possessed a similar disposition, 

 provided they were coloured. 



Stems are sometimes directed towards the earth, in which they 

 attempt to bury themselves, like roots ; a phenomenon worthy of the 

 greatest attention, not only on its own account, but for the sake of the 

 circumstances connected with it : many vegetables, besides their 

 above-ground stems, have also subterraneous stems. These creep 

 horizontally in the interior of the earth, without manifesting any 

 tendency towards the sky. They are white, like roots, of which they 

 assume the course and the station. Sometimes, however, they are 

 pink, as in upright burreed : in such cases it is the rind that is 

 coloured, and not the pulp beneath ; but, whenever the point of their 

 stems approaches the surface of the soil, it becomes green ; and from 

 that moment they acquire an upward tendency. 



Stems are generally directed towards the light, in accordance with 

 their colour, which is usually green ; while the roots have usually a 

 tendency to avoid the light, which coincides with their want of colour. 

 The colour of the roots is, in fact, nothing but that of the vegetable 

 tissue ; and can by no means be compared to that of the petals of 

 some plants, which arises from the presence of a white colouring 

 matter. Light, which is the principal, but not sole, cause of the 

 colour of stems and their organs, has no power of infusing colour into 

 the roots, as may be easily seen by roots growing in glasses of water. 

 In spite of the influence of the light, they constantly remain colour- 

 less ; and this does not depend upon immersion in water, because 

 leaves, developed in that medium, are nevertheless green. Although 

 roots have, in general, no tendency towards the light, yet such a dis- 

 position does become manifest, provided the terminal shoot of a root 

 becomes slightly green, as occasionally happens. Having induced 

 some seeds of marvel of Peru to germinate in damp moss, I remarked 

 that the young roots, when about as long as the ringer, were terminated 

 by a shoot of a slightly green colour. Wishing to know whether these 

 roots would turn towards the light, I placed them in a glass vessel 

 filled with water, having a wooden cover pierced with holes to receive 

 the roots, and fix the seeds. I enveloped the vessel in black cloth, 

 leaving only a narrow vertical slit, through which light could enter the 

 interior. This slit was exposed to the rays of the sun j and, a few 

 hours after, I found that all my roots had hooked back their points 

 towards the slit through which light was introduced. The same ex- 



