CHAP. II.] CHEMISTRY, ETC., OF PLANT LIFE. 79 



sections. (1) Parasites, plants that obtain their food 

 from the bodies of living plants or animals ; as examples 

 may be mentioned the various species of broomrape 

 (Orobanche), the dodders (Ouscuta), and numerous spe- 

 cies of fungij as the mildews causing the potato disease, 

 also that of the hop, vine, etc., to which may be added 

 those fungi popularly known as " rust,'^ " mildew," and 

 "bunt,^' that are so very destructive to many of our 

 important cultivated plants, more especially the cereals. 

 Several species of fungi grow on the bodies of living 

 insects ; the disease known as " muscardine," that com- 

 mits such havoc with the caterpillar of the silkworm 

 moth, is caused by a fungus. The plant or animal to 

 which the parasite is attached, and from which it derives 

 its food, is termed the host, a term which, if plants could 

 express their, feelings, would probably be considered as 

 sarcastic, inasmuch as the hospitality is altogether invo- 

 luntary, and greatly to the detriment of the host. 

 Parasitism is an acquired function. Parasites occur in 

 natural orders of plants that are widely separated from 

 each other, proving that this function has originated 

 independently at many points, and, judging from the rela- 

 tive amount of modification presented by different plants 

 for the purpose of enabling them to hold their own 

 under the new conditions imposed by becoming para- 

 sites, it would appear that this retrogression or falling 

 back from the characteristic mode of plant nutrition had 

 occurred at widely- separated periods of time ; but this 

 need not necessarily be so, as it is well known that 

 plants, like animals, vary to a very marked extent in 

 their power of adaptation to changed conditions, some 

 that possess what may be termed an elastic constitution. 



