Chapter Twenty 



PLANT HORMONES 



Hormones as growth regulators (151). Vitamins (152). Plants as a 

 source of hormones ( 154). Work with the oat coleoptile ( 154). Root- 

 ing cuttings with chemical stimulants (156). Possible advantages of 

 root stimulation (156). 



Chapter Twenty-One 



SOIL IMPROVEMENT 



Importance of good texture (158). Water-holding power of the soil 

 (160). Value of humus (161). Compost (161). Living organisms 

 (162). Soil erosion (162). 



Chapter Twenty-Two 



FERTILIZERS 



Essential elements (164). Why plants need fertilizers (165). The 

 function of each element (169). The application of fertilizers (170). 

 Lime (171). The newer methods of growing plants in water solutions 

 of fertilizers (172). 



Chapter Twenty-Three 



NITROGEN 



The carbon/nitrogen ratio of Kraus and Kraybill (175). Nitrogen and 

 growth (176). Means of supplying nitrogen (176). The nitrogen 

 cycle (178). 



Chapter Twenty-Four 



SOME SPECIAL CONSIDERATIONS OF PLANT GROWTH 



Light and Growth (181). Description of growth (182). Temperature 

 and growth (183). Water and growth (184). Growth cycles (186). 

 Regulation of growth (186). 



Chapter Twenty-Five 



REST PERIOD OF PLANTS 



Seeds, bulbs, grass and trees in the dormant condition (188). Physiol- 

 ogy of dormancy (189). Breaking the rest period (190). Using the 

 rest period (191). 



Glossary ( 193 ) 



