32 The Growth of Seeds 



would find that as the roots grew, instead of growing 

 out straight, they curved right round with their tips 

 pointing to the earth. They soon straighten themselves 

 out again when they are put the other way up, and 

 again point downwards. All roots possess this strange 

 property of being drawn towards the centre of the 

 earth. Exactly the same thing happens if an acorn is 

 planted upside down. As soon as the root shows itself 

 it begins to curve round towards the earth. This is 

 very useful, as, whichever way up an acorn is when it 

 falls, the root always grows down into the ground. This 

 property is called by a long name, geotropism, meaning 

 turning to the earth. It has never been altogether 

 explained, but is known to be connected with the force 

 of gravity which tends to draw everything to the earth. 

 If a growing seed is placed on a revolving table and is 

 made to turn round and round by clockwork, then, in 

 much the same way as a stone tied to the end of a 

 string and whirled round your head pulls outwards, the 

 root instead of growing towards the ground will grow 

 straight out, away from the centre of the circle in which 

 it is turning. This sensitive behaviour is found to belong 

 to the very tip of the root. Other properties which it 

 has and which you will see are very useful to it are those 

 of growing away from the light and towards moisture. 



If you look closely at the root of your bean you will 

 notice something that looks like a thin layer of gum 

 covering part of it. This layer really consists of 

 enormous numbers of tiny hairs, so tiny that it is 

 impossible to distinguish them without the help of a 

 microscope. They are* called root hairs, and their 

 business is to suck up the water and to pass it on to 

 the growing plant. They are so small that they grow 



