8 Diseases of Greenhouse Crops 



to secure proper control of his soil and to make it 

 ideal for plant growth. 



A. Bacteria. Bacteria are minute microscopical 

 plants that consist of a single cell. They are com- 

 posed of a cell wall of protoplasm and average about 

 1/25000 of an inch in length. These simple organ- 

 isms multiply by fission, that is, the original mother 

 cell divides in two equal parts, which may separate 

 or remain united, giving the appearance of a thread. 

 It has been estimated that a single bacterium divides 

 about every twenty minutes. Granting that this 

 rate of division is uninterrupted for twenty-four 

 hours, the descendants of a single one within a day 

 would be in round numbers 1,800,999 trillions. 

 These when placed end to end would make a string 

 two trillion miles long, or a thread long enough to 

 go around the earth at the equator 70,000,000 times. 

 However, multiplication at such a rate cannot occur 

 because food conditions are restricted. The three 

 main types of bacteria are: 1. the cocci, 2. the ba- 

 cilli or rods, 3. the spirilla or spirals (fig. 2, c). 

 The greater number of the soil bacteria are benefi- 

 cial, the most common being the saprophytes, or 

 those which help to decay the dead organic matter 

 from either animal or plant. The parasites on the 

 other hand are those which produce disease. 



B. Fungi. Fungi are low forms of microscopic 

 plants, of a slightly higher type than bacteria. Fungi 

 are made up of colorless feeding threads technically 

 known as hyphae or mycelium. The spores which 

 correspond to the seed of the higher plants are borne 



