ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



In dealing with those animals that feed upon plants it is 

 impossible to draw any clear line between vegetarians and para- 

 sites. We shall, however, be justified in applying the latter name 

 to a number of small forms which live, generally for part of their 

 lives only, within the tissues of plants, one consequence being 

 the formation of certain abnormal growths. Some of these will 

 be dealt with later on in connection with the subject of agricul- 

 tural pests. The clubbing of turnip-roots (" finger-and-toe " or 



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Fig. 1073. Bacteria, i, The "blood portent ' (Micrococcus prodigiosus]; 2, gelatinous stage of the same. 

 3, Bacteria which produce acetic acid (Bacterium aceti}; 4, the same on larger scale. 5, Bacteria of Asiatic 

 cholera (Spirochcete cholera; asiaticce]; 6, the same on larger scale. 7, Anthrax bacilli (Bacillus anthracis] 

 with red blood-corpuscles; 8, the same on larger scale. 9, Bacteria of relapsing fever (Spirochcete Obermeieri] 

 and red blood-corpuscles. 10, Symbiotic bacteria (Sarcina ventriculf] from human stomach, i, 2, 3, 5, 7, 

 and 9, X 300. 10, X 800. 4, 6, and 8, X 2000. 



" anbury "), for example, is caused by one of the Fungus- Animals 

 (Plasmodiophora brassicce), which interferes with the nutrition of 

 the plant, causing it to grow in an unusual way. And it not 

 infrequently happens that cereals and some other cultivated forms 

 are attacked by small Eel-Worms, the presence of which has a 

 stunting or distorting effect. 



Most persons have noticed the curious local outgrowths known 

 as " galls " that are common upon some plants, and tempt com- 

 parison with the tumours and cancers of animals. They are due 

 to the attacks of Gall- Flies, small forms belonging to the order 

 of Membrane- winged Insects (Hymenoptera). The female gall- 



