CHAPTER EIGHTEEN 



DISEASES OF PLANTS 



As a Blight is the most common and dangerous Distemper 

 that Plants are subject to, so I shall endeavour to explain 

 by what Means Vegetables are affected by it ; and if I shall 

 be so happy, from the Observations I have made, to dis- 

 cover the Cause of it, the Remedy may then be more easily 

 found out, and the Gardener will with more certainty hope 

 for Success from his Care and Labour. 



From an Old English Garden Book (1726) 



ALL the vegetables of the garden are plants that 

 have roots, stems, and leaves. Each of these parts has 

 different work to do ; and in the plants there are vessels 

 to carry water, minerals, and foods between the different 

 parts. 



The garden plants all have chlorophyll, a green color- 

 ing matter which makes them able to use the energy of 

 the sunlight in building food. They are, therefore, self- 

 supporting ; they can make their own food from carbon 

 dioxid taken from the air, and from water and minerals 

 taken from the soil. As we have learned in earlier 

 chapters, this is one of the main reasons why they are so 

 valuable to man as food plants. 



The garden plants also produce seeds, which usually 

 pass through a resting period before the young plants 

 resume growth. In this way the plants that live but 

 one year are able to pass the winter months. 



In all these respects garden plants are like the many 

 kinds of trees, shrubs, and herbs that are abundant and 

 conspicuous all about us. Because of these qualities, 

 and especially because of their power to produce seeds, 

 these plants are considered to be the higher forms of 



plant life. 



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