AGRICULTURE. 



spores (seeds), which will settle on other leaves, 

 and thus cause the spread of the disease. A 

 ragged hole will remain in the leaf, usually brown 

 in color on the margin 



disease in vegetation are all minute plants. These lower forms of 



plants live in and upon the higher plants, taking the food 



out of the plants and 



thereby checking 



their growth and even 



killing them. Where 



did they come from ? 



The field crops grow 



from seeds, and when 



they are ripe, they 



produce Other Seeds Fig. 42. A diseased leaf. The minute plant causing 

 disease is growing in a leaf and is throwing off ripe 



that will again grow. 

 Now these small 

 plants, these disease 

 plants, grow from tiny seeds generally called "spores," and 

 when they mature they form other spores which will be carried 

 about by the wind, settle on other plants, start growing there, 

 and thus spread themselves. A small dark speck appears on 

 the leaf of a house plant the spore has started to grow. The 

 speck grows to a large spot, it soon becomes darker, then the 

 whole spot or scab breaks open the spores are ripe and fall 

 off or are blown away, and the life of this disease plant begins 

 again on another leaf or on another plant. Why did we not 

 see the spores at first ? Simply because they were too small, 

 they can be seen only by a magnifying glass or a microscope 

 hence these plants are sometimes called microscopic plants. 



PREVENTION OF DISEASE. If we could destroy these spores 

 we would, of course, prevent the growth of the disease plants. 

 In addition, therefore, to destroying all plants and parts of 

 plants known to be diseased, we should use preventives when- 

 ever we think the disease is likely to be started. The leaves 

 and stalks of house plants are washed from time to time in 

 order to clean them from dust and also to wipe off disease 

 spores. One of the principal substances used for killing these 



