5o6 



Marvels of the Universe 



and the roots straight down into the water. '^Xow by adjusting the cloth, allow the light to stream 

 in from one side only through a narrow slit. In a few hours a remarkable change will have come 

 over the little plants. The shoots will be leaning over to the direction from which the light has 

 come, and the roots will be curving away towards the darkness under the cloth-covered part of the 

 shade. Obviously the roots have a distinct tendency to grow away from the light. 



One is at a loss to explain the causes of this light-avoidance on the part of plants, although the 

 purposes which are served thereby seem in most cases to be fairly clear. There is a still more 

 baffling problem before us when we come to consider the case of those plants which produce organs 

 capable of both light-seeking and light-avoiding, according to circumstance. In two accompanying 



illustrations are shown the flowering points of 

 the well-known Rose of Sharon. Now in the 

 first picture it will be noticed that the stem 

 producing the bud is curved very decidedly in 

 an upward direction. This habit of growth 

 towards the light ensures that the flower shall 

 be properly displayed. It is not very long 

 after the flower is over and the seed has been 

 set that a striking change is seen to be taking 

 place in the bearing of that which is now a 

 capsule. Gradually the stem turns round, 

 growing away from the light until it arrives at 

 an entirely different position ; instead of being 

 curved upwards, it is bent down towards the 

 soil. It now only remains for the capsule to 

 open in order that the seeds may pour out on 

 to the ground in such a way as would not have 

 been possible without this change in the bearing 

 of the stalk. We may find another instance 

 of a similar nature in the case of the ivy- 

 leaved toad-flax. This little plant, which is so 

 abundant upon old walls, must be very familiar 

 to e\-eryone. If an example be examined, it 

 will be noticed that when the small purple 

 flowers are in their full beauty, the stem bear- 

 ing them bends in a pronounced style towards 

 the light. After the setting of the seed, should 

 the case continue to be held in this fashion, 

 there would be small chance that the contents 

 would find a suitable resting-place. Most 

 probably they would tumble to the ground, where they would be unable to grow into mature plants, 

 on account of the coarse weeds and grasses with which they would be surrounded. But just at 

 the time when the seeds in the capsule are getting ripe, the stem changes its habit and shows a 

 strong tendency to grow away from the light. In this way the case is brought round into close 

 contact with the wall, and by the time the actual dispersal takes place, it would not be easy for 

 the seeds to do other than fall into some crevice. Thus, wdren the seeds germinate, the little plants 

 will find themselves in an ideal situation for their peculiar habits of growth. 



Whilst admiring such beautiful arrangements as these, the student cannot well refrain from asking. 

 How is this change of bearing brought about ? It must be confessed that at present it is not possible 

 to offer any solution which will in any way supply a sufficient reason. The great botanist, Kerner, 



Fholo 61/] 



r-"-'. /-. /in.</l«. 



LIGHT AND THE PLANT. 



Mustard-seed has Were been sown on nnuslin stretched over a 

 tumbler, and the light has been allowed to penetrate to the 

 seedlings from the left-hand side. Notice that the leaves lean 

 towards the light and the roots turn away. 



