PAEASITISM 



295 



wMcli penetrate to, and tap sap in, the vascular bundles. 

 It is now established and on the strength of another's 

 labour it branches and extends with astonishing 

 rapidity, grasping other hosts in the neighbourhood, and 

 extracting food with ignoble industry. Fortunately the 

 Dodder is an annual; its cycle of existence is completed 

 in a single season, but it develops a large number of 

 flowers and an abundance of seeds, which perpetuate its 

 kind. Agriculturalists are apprehensive of the Dodder, 

 and if they are wise wage 

 relentless war against it. 

 The student of flower- 

 ing parasites will observe 

 that, in consequence of 

 the parasitic habit, in- 

 volving the loss of ability 

 to manufacture food in 

 the normal way of green 

 plants, there is a great 

 reduction of leaves. In the Dodder aU that is left to 

 indicate ancestral foliage is seen in very small yellowish 

 scales. In some species the stems also are much reduced, 

 while in the tropical Rafflesias the flower is practically 

 the whole plant. Raffiesia Arnoldi (Fig. 80) is the 

 largest known flower; it is over a yard across. It grows 

 in Sumatra. Quite stemless, it rests immediately upon 

 roots of species of Gissus, from which it extracts the 

 nutriment necessary for its giant form. The rapid 

 growth of some parasites, and their prodigality in 

 reproduction, remind one that " ill weeds grow apace " 

 — an adage which the reader will agree is applicable to 

 other than parasites of the vegetable kingdom. 



Fig. 



80. — ^The Pabasete Raitlesia 



AE.NOLDL 



