THE BOOK OF NATURE STUDY 



The lines should be very carefully drawn to the very tip of the 

 radicle. At the end of twenty-four hours the distances between 

 the lines, which at first were equal to each other, are now very 

 different, the greatest distance occurring 

 near the tip of the root. This experiment 

 shows that growth is most active just be- 

 hind the tip of the root. 



Another plan is to grow the bean in 

 sawdust, then to mark the radicle with 

 equidistant lines, and to examine the radicle 

 at the end of every six, twelve, and twenty- 

 four hours. Pfeffer in his Physiology of 

 Plants (vol. ii. p. 8) gives a seedling of vetch 

 (Vicia Faba\ in which the end of the root 

 had grown 4-6 millimetres in six hours and 

 20 millimetres in twenty-four hours. 



Sometimes seeds do not give the ex- 

 pected results in moist air ; when this is the 

 case it is generally due to the air not having 



beCn ^P 1 m ist > Water haS been lost b ^ 



marked with trans- evaporation and by absorption into the seed, 

 verse lines to show an d has not been renewed. The advantage 

 the region of greatest f fe t air over sawdust is, that if the 



growth. . > 



seeds are suspended in moist air to the 

 cork of a bottle, they can be examined without disturbing 

 them. 



ACTION OF GRAVITY ON ROOTS. That roots grow downwards 

 owing to the action of 

 gravity may be demon- 

 strated to a class by 

 means of a simple form 

 of clinostat. A con- 

 venient form of this 

 instrument has been 

 introduced by taking 

 a strong eight-day clock 

 and fastening to the FIG. 8. Clinostat. 



FiG. 7 .-Radicleofbean, 



