REGIONS OF GROWTH 99 



its being touched, and leave for the night; By 

 morning the end will have turned upwards, and you 

 will find by looking at the marks that it is only the 

 youngest parts, those internodes which are still in the 

 process of lengthening, that bend ; the older parts 

 that have finished growth do not move. 



If you have another plant treated in the same way but 

 standing vertically, you will find that the lines on the 

 lower side of the curved end of the horizontal plant are 

 further apart than those in a similar position on the 

 upright plant ; which shows that the lower side of the 

 horizontal plant is somehow stimulated to grow a little 

 faster than it would otherwise have done. 



This experiment is a very easy one and should be 

 made without fail. You may do the same with the 

 root. The best way is to take a large seed, such as 

 the Broad-bean, and, after it has begun to germinate, 

 and the radicle is about 1 inch long, to mark it in 

 the same way with very thin lines at equal distances 

 of TF inch and then fix the seed by a strong pin with 

 the root horizontal, on the under side of the cork of 

 a wide-mouthed bottle. Put a little water in the 

 bottle to keep the air moist, and cover all over to 

 keep out the light. In a few hours the tip will have 

 begun to bend downwards and will go on growing 

 downwards. You may turn the bottle round, so that 

 the tip of the root is again horizontal, and it will 

 again bend downwards. No matter how often you 

 repeat the experiment you will find that it is only 

 that part which, as shown by the marks, is growing 

 longer that bends down the older parts which have 

 ceased to grow are incapable of bending. 



