Bower • Parasitism in Flowering Plants 



35 



F. O. Bower 



Parasitism in Flowering Plants 



Reprinted from Chapter 23 of Plants and 

 man. London, Macmillan Company, 1925 

 with the permission of the representatives of 

 the late Dr. Bower. 



In human society a brigand is not 

 merely regarded as a moral delinquent; 

 he is held to be an enemy of the State. 

 The foundation for this lies ultimately 

 in Man's consciousness and volition. It 

 is from his possession of these powers 

 that the social order which recognizes 

 public and private rights has sprung. In 

 plants there is no evidence of either 

 consciousness or power of volition, nor 

 consequently of moral sense. In a 

 crowded flora there is ruthless compe- 

 tition for any suitable nourishment 

 that may be available, and the prize 

 naturally falls to the plant that has the 

 strongest absorptive powers. Conse- 

 quently parasitism, or physiological 

 brigandage, may follow at any point 

 where contact results from overcrowd- 

 ing, provided that one of the organisms 

 in contact has more power to retain 

 it. Such opportunity is general; very 

 naturally, therefore, the origin of para- 

 sitism does not appear to have been 

 restricted to any definite place or 

 period. Nor is it restricted to any one 

 group of organisms. It is true that the 

 most tvpical instances of the habit are 

 found among the Fungi, plants prob- 



ably of Algal origin, which have ex- 

 isted from vet)' early times. But many 

 genera of Flowering Plants belonging 

 to divers families show it; and this in 

 itself suggests that in them the habit 

 has been relatively recently acquired. 

 Parasitism being thus a phenomenon 

 of sporadic origin, it is difficult to speak 

 of it effectively in general terms. It will 

 be better to study concrete examples: 

 and for simplicity of description to 

 choose them first from Flowering 

 Plants. 



The Convolvulaceae provide a good 

 instance of the way in which a climb- 

 ing habit may lead to full parasitism. 

 The common Bind Weed or Con- 

 volvulus is a spiral climber, whose thin 

 whip-like stem twines round its sup- 

 port, so that its living tissue comes into 

 very close contact with the outer sur- 

 face of the host. But the advantage it 

 derives is merely mechanical; it is well 

 able to nourish itself by its large green 

 foliage leaves, and by supplies of salts 

 brought up from the soil by the roots. 

 But the genus Cuscuta, the Dodder, 

 which is referred to the Convolvulus 

 family because its flowers are of that 



