;o2 



Marvels of the Universe 



PLANTS WHICH SEEK AND AVOID THE LIGHT 



BY S. LEONARD BASTIN 



It does not take long for the student of Nature to discover that there are a great many things in 

 this wonderful world which no one can explain. There is little doubt that some of the most per- 

 plexing problems arise in the case of plants, more especially where the question of relation to 

 environment is concerned. No longer is it possible to regard the plant as a kind of living machine, 

 where there is nothing to consider but a question of mere cause and effect. Such a point as this 

 can scarcely be better illustrated than by the behaviour of plants in connection with the presence or 

 absence of light. 



Now, in a general wav, it is quite true that plants desire as much light as possible. Everyone 



has noticed the manner in which 

 the window geraniums of the 

 cottager grow. Unless the house- 

 wife takes care to turn the speci- 

 mens from time to time, the 

 development will be all on one 

 side — the foliage and, finally, 

 even the stem of the plant lean- 

 ing awav from the darkness of 

 the room towards the light 

 quarter. Plants in shady places, 

 such as at the bottom of hedges, 

 grow tall and spindly, and so 

 bring their foliage up to the 

 necessary light. In a measure 

 the phenomenon is explained by 

 the fact that the extension of 

 vegetable tissue takes plaice more 

 rapidly where there is little light 

 than in situations where the 

 illumination is ver\- brilliant. 

 This will help us to understand 

 how it is that the geraniums 

 already mentioned grow^^to the 

 window. On the shady sides 

 of the leaf-stalks growth will be 

 Naturallv this causes the stalks to bend 



Pholo by\ [■'••. /-. rindin 



LIGHT AND THE PLANT. 



New. Zealand \ eronica growing wilh the leaves one above the other to 

 shield them from the sun 



The 



more rapid than on the sides which are well illumuiated. 

 over in the manner which has been noticed, although it should not be assumed that we have 

 here a complete explanation. Even at the threshold of our study of these light-seeking and light- 

 avoiding plants, we must confess that we do not know the whole story. Apart from the stalks, 

 it is easy to see that the leaves themselves seem to twist round, so as to bring their upper surfaces 

 into full illumination. The point is also well illustrated in the case of many climbing plants, such 

 as ivy and the ampelopsis creeper. We may saj? that the tissue of the leaf responds to the action 

 of the light, but this is only a roundabout way of putting that whicli we alreadv know well. 



Some kinds of seedlings show an astonishing sensitiveness to light. Darwin has described the 

 manner in which the first leaves of certain grasses will bend towards a distant lamp which emitted 

 so little light that a pencil held close to it did not cast an\- shadow on a white card. The great 



