504 



Marvels of the Universe 



Photo by'] 



of the Ne 



LIGHT AND THE PLANT. 



Zealand Veronica taken from 

 the parallel of the leaves. 



[.S". L. Bmlin. 



scientist has also shown us how 

 seedHngs, kept in a dark place, and 

 laterally illuminated for two or 

 three minutes at intervals of about 

 three-quarters of an hour, bowed 

 towards the direction from which 

 the intermittent light had come. 



Sunshine is, of course, a necessity 

 if plants are to carry on the forma- 

 tion of their green matter but it is 

 possible to have too much of e\'en 

 this good thing. Such an effect is 

 most commonh- to be seen in the 

 warmer countries of the world, and 

 the outcome is peculiarly striking in 

 Australia, where, of course, the sun 

 is at times nearly overhead. The 

 fierce rays pouring down upon the 

 surface of the foliage are very 

 harmful in their effects upon the 

 delicate chlorophyll, and as well an 

 undue transpiration of moisture is 

 likely to take place. The situation 

 has been well met by an arrange- 

 ment whereby nearly all the 

 Australian trees and shrubs present 

 their lea\-es edgeways to the sky. The broad expanse of the organs is not exposed at all to the 

 direct rays of the sun, save in the morning and evening, when the amount of light and heat is 

 somewhat lessened. Those who have travelled in Australia say that the forests of eucalyptus and 



acacia cast a small amount of shade 

 compared with that afforded by 

 trees in more temperate regions. 

 It is a singular fact that the foliage 

 of the seedling eucalyptus trees is 

 held in a horizontal position ; not 

 until the third or fourth year will 

 the mature type of leaf be pro- 

 duced. Although the shade under 

 the parent tree may not be very 

 dense, 3-et the youngsters will 

 certainly receive the sunlight in 

 a very much modified form. In 

 order to secure enough for their 

 purposes it is necessary that they 

 should expose their full surfaces 

 upwards. 



We need not, however, go to 

 the other side of the world to find 

 instances of plants which in some 



Fhoto hu'] [.S. L. Jiaslia. 



LIGHT -AND THE PLANT. 



A seedling V'eitch's Creeper has here been grown in a box to sho\v that the 

 leaves turn to the light while the tendrils turn a^vay from the light. 



