12 GARDEN FARMING 



as in the flowers, where they give the pleasant odor which is char- 

 acteristic of many plants. The oils which give the perfumes are 

 called essential oils. These oils are volatile at ordinary tempera- 

 tures ; they make an impression upon the sense of smell and give 

 us the odor which is either pleasant or offensive. 



Other things being equal, the greater the food supply, including 

 moisture, with congenial atmospheric conditions, the more rapid 

 will be the development of plant tissue, and consequently the more 

 rapid the growth of the plant. In commercial market gardening or 

 truck farming quick growth is as a rule the result desired. 



Plant diseases. It is a misfortune that there are such things as 

 diseases of plants, but every commercial grower of plants is familiar 

 with a greater or less number of discouraging factors, either in the 

 form of plant diseases or insect enemies. Plant diseases, as we 

 recognize them at the present time, are the results of low forms 

 of plant life, that is, parasitic plants which live upon the growing 

 tissue of other plants instead of deriving their nourishment directly 

 from the soil or from dead and decaying plant tissue. These low- 

 form parasitic plants are known under different generic names, 

 but, collectively, they may be spoken of as fungous diseases and 

 bacterial diseases. 



It is not necessary for us to go into the distinction between these 

 types of plant diseases ; it is sufficient to note the manner in which 

 they act upon their host plant and interfere with its growth and 

 profitable development. In general they act in two ways. They 

 either break down the tissue of the leaves and thus interfere with 

 the nutrition of the plant by dwarfing and stunting its growth and 

 curtailing its ability to elaborate the crude materials provided by 

 the roots ; or they gain an entrance to the ducts and passages 

 of the interior of the plant, and by their growth and development 

 clog these passages so as to cut off the flow of crude material 

 gathered by the roots for the use of the leaves. 



As a general thing, the fungous diseases attack the plant from 

 the outside, while the bacterial diseases work upon the inside. 

 What has already been stated is sufficient to indicate the importance 

 of a knowledge of the behavior of plant diseases in determining 

 the method of their control. It is evident that diseases which attack 

 the plant from the outside can be resisted by placing upon the 



