OTHER METHODS OF OBTAINING FOOD 219 



Some curious parasites which are met with in the 

 tropics show a very peculiar method of attaching them- 

 selves to their host plant. They constitute the natural 

 order Eafflesiacece. The embryo, after emerging from the 

 seed, penetrates the cortex of its host, usually a root, though 

 not always, and gradually forms a hollow cylinder surround- 

 ing its woody centre. This sheathing structure is com- 

 posed of rows of cells, and in appearance resembles the 

 mycelium of a fungus. Buds arise upon this investment, 

 which eventually burst the cortex above them, and protrude 

 through the host plant. These, in Bafflesia itself, develop 

 a single flower which, in some cases, is of enormous size. 

 The plant produces no outgrowths of any kind except the 

 buds described. Other genera show some modification of 

 this structure, but exhibit exactly similar physiological 

 peculiarities. 



Certain other parasites which resemble these in many 

 respects differ in attacking only sub-aerial portions of their 

 hosts. The most easily observed of these is the Dodder 

 (Cuscuta), which often attacks the clover (fig. 105). The 

 seed when germinating puts out an embryo which bears no 

 cotyledons. Germination takes place on the ground, and 

 the embryo grows to a length of about an inch. Its apex 

 attaches itself to the ground, and the free portion moves 

 round, describing a sort of spiral in the air. If it comes in 

 contact with a suitable host, it twines round it after the 

 fashion of a tendril, and numerous suckers are developed 

 in rows at the points of contact. Haustoria spring from 

 these suckers and penetrate the host, extending inwards till 

 they reach the wood (fig. 106). The part below the attach- 

 ment dies shortly after this relationship has been esta- 

 blished, and the parasite is left attached to the host. In 

 its further growth it continues to twine around the latter, 

 putting out numerous branches, which also form similar 

 coils, so that the host is completely immeshed in the 

 twining stems of the parasite. The latter bears no leaves 

 and possesses no chlorophyll in any part, so that it derives 



