126 



Commercial Gardening 



00 



' 2 3 



Forms of Bacterial Cells 

 1, Coccus. 2, Bacillus. 3, Vibrio. 4, Spirillum. 



a a' a" 



o 

 b 



b' 



OO 

 b" 



and cease to grow. The sudden change from say 80 to 50 F. would 

 injure the active bacteria and put them completely out of action, with 

 the result that food supplies are immediately cut off from the plants. 

 One of the great problems the cultivator has constantly before him there- 

 fore is to maintain just the temperature to promote the greatest activity 

 amongst the soil bacteria. The grower under glass succeeds in doing 

 this often at a great cost; but the open-air grower must make use of 

 hot beds and plenty of good manure to achieve favourable results. 



There are several kinds of 

 nitrate-forming bacteria in pro- 

 perly cultivated soils, amongst the 

 best known to scientific research 

 being Bacillus mycoides, B. mes- 

 entericus vulgatus, B. subtilis, 

 and Proteus vulgaris. With a 

 proper supply of organic manure, 

 a certain amount of lime to check 

 acidity, a genial temperature, and 

 a deeply worked soil these bac- 

 teria render valuable services. 



In The Standard Cyclopcedia 

 of Modern Agriculture we are 

 told that "bacteria have a very 

 simple structure a speck of liv- 

 ing protoplasm surrounded by a 

 capsule or cell wall. They are 

 unicellular, and are the smallest 

 living organisms known, some 

 being less than a6 ooo in. in dia- 

 meter. Although there are hun- 

 dreds of different species, there 

 are only three general forms the 

 spherical (termed a coccus), the 

 rod-shaped (termed a bacillus), 

 and the spiral (termed a spirillum). 

 A curved rod is termed a vibrio." Professor W. B. Bottomley once 

 humorously classified the three kinds billiard balls, cigarettes, and cork- 

 screws. The diagrams (fig. 90) illustrate the various forms and the methods 

 of vegetative reproduction. 



A single bacterium dividing in two, and taking one hour for the com- 

 pletion of the process, will in twenty - four hours produce 16,000,000 

 under suitable conditions. In ordinary cultivated soil the number of 

 bacteria varies from 300,000 to 10,000,000 per gramme of soil (100 gm. = 

 3'527 oz. avoir.). They occur in the greatest number in the first 6 in. 

 of the soil; below this they rapidly diminish until at a depth of about 

 3 ft. very few are to be found. Professor Hilgard, of the Calif ornian 



ee 

 C" 



C 1 " 



Fig. 90. Diagrammatic Representation of the Methods of 

 Vegetative Reproduction among Common Bacteria 



a, A bacillus successively dividing at a 1 , a", and a 111 . 

 6, A coccus giving rise to chains, &'" (Streptococci) ; pairs, 

 6 IT (Diplococct) ; and irregular groups, 6 V (Staphylococci). 

 c, A coccus giving rise by division in two directions to c 1 " 

 (ificrococci), and by division in three directions to c lv (Sar- 

 cince). 



