CH. ij Qualitative Differences y 



All these results are shown in the curves of Fig. 6. 

 But there is something more than actual weight. The 

 student who carries out the experiment will observe 

 that some of the plants differ very much in appearance 

 and agricultural or horticultural value even when their 

 weights are not unlike. Between Pots 3 and 7 (Fig. 5), 

 for instance, there are great differences. in appearance 

 and habit of growth. Pot 3 (5 per cent, of water and 



u 



*^ . 



S c3 



20 



lOr 



Sand 



>;-02 



-!<0 



73 

 o 



'5 



O 



ft 



<o 



-IJ IB 



H 



a 2 

 >.^ 



u 

 ^3 



O 



SO 



30 



20 



10 



Soil 



10 Water 



10 Water 



Fig. 6. Curves showing weights of crop produced with varying supplies 

 of water and 0, 0-01 and 0-02 gram of nitrate of soda per pot. 



no nitrate) contains sturdy plants capable of great 

 development if transplanted into more favourable con- 

 ditions, while Pot 7 (12| per cent, water and no nitrate) 

 contains "leggj^" plants that would never be of any 

 value. Similarly the wetness of the soil affects the root 

 development : in a dry soil there is more root than in a 

 wet one: von Seelhorst showed that barley growing in 

 a soil watered only to half its full water-holding capacity 

 produced twice as much root as when the water was 

 maintained at three-quarters the full capacity. These 

 differences are highly important from the practical point 



