THE WORK OF ROOTS 89 



this starts the growth in the right direction. This 

 idea may be tested by a very simple experiment. In 

 a small saucer, place some mercury; fasten two or 

 three clothes-pins to the side of the dish (Fig. 74) ; to 

 these pin germinating 

 seeds (Peas are especially 

 good) with perfectly 

 straight caulicles about 

 half an inch long; let the 

 caulicles, especially at the 



- - _ 74. Seeds arranged with their caulicles 



tip, rest on tne SUriaCe OI resting on mercury, •which is covered 



the mercury. Pour in with a mtie water. 

 enough water to partially submerge the seed. If, now, 

 the root -tip bends downward into the mercury, over- 

 coming its resistance, the idea that it droops of its own 

 weight cannot be correct. If the mercury is not clean 

 it may kill the root, since mercury salts are poisonous ; 

 it is well, therefore, to first clean the mercury with a 

 little cotton wool, and afterwards with running water. 

 In place of mercury we may use gelatine (one part of 

 gelatine dissolved in five of water), in which case no 

 water is to be placed in the dish, but it should be 

 covered with a piece of glass to prevent the roots from 

 drying up. 



What starts the root in the right direction? Is it 

 light, moisture, air, warmth, food or gravity ? We 

 may test the first five simultaneously by a very simple 

 experiment. Fill a box (having a bottom of wire 



