PRODUCING DISEASE RESISTANT 

 PLANTS 



By Casper L. Redfield. 



A PLANT is an organism composed of many cells. In 

 '*^- tlie growing part of the plant these cells are living things 

 which have w-ithin them certain powers. A plant disease is 

 a conflict, or the result produced when these living cells are 

 attacked by parasites which are themselves living cells. If 

 these parasites are sufficiently numerous, and have greater 

 powers of attack than the plant cells have of defense, then the 

 plant dies. If the parasites are not numerous, or have less 

 powers than the cells of tlie plant have, then the plant is affect- 

 ed little or not at all by the attack. 



Plants are of many kinds and diseases are of many kinds, 

 1)ut as we are not going into the technicalities of any particu- 

 lar disease, we will refer to plants and diseases in a generic 

 way. A particular plant may have the power of resisting 

 one disease and not the power of resisting another disease. 

 In other words, disease resistance is specific, and the fact 

 that a plant has the! power of resisting one disease does not 

 give it the power of resisting some other disease. Also, the 

 power of resisting a particular disease is specific for the plant 

 which has it. One plant of a variety may have such great 

 power of resisting some particular disease that it is said to 

 be immune, and another plant of the same variety may have 

 so little power of resisting the same disease that it is said to 

 have none at all. 



These cjualitics of resistance and susceptibility are in- 

 herited (|ualities. The progenv of resistant plants are resis- 



