654 THE LIFE-HISTORY OF LORANTHUS EXOCARPI BEHR, 



length of the branch. The excrescence is increased in bulk by 

 thin sheets of the parasite growing outward from the central 

 mass. These reaching the exterior of the swelling, become 

 covered by bark. Excrescences have been observed with a 

 diameter of six inches, though this is an exceptional size for this 

 species. 



In many instances, however, the portion of host- wood between 

 the sheets of Loranth-tissue becomes submerged, owing to the 

 cells of the parasite invading the cambium, and thus stopping 

 further outward growth of the host. If the excrescence be cut 

 through, portions of the parasite will be noticed, which have to 

 all appearances grown from the exterior towards the centre. 

 These vary in the depth to which they have penetrated, some just 

 entering the sapwood, others with several annual rings of the host 

 above their points. What really happens is that the Loranth cells 

 invade the cambium, become lignified, and are built round by the 

 annual growth of the host. Every annual ring buries the parasite 

 deeper within the host; but, unlike the European species, it does 

 not produce a root-system, like those mentioned by Kerner and 

 Oliver, which invades the cambium cells of the host, either above 

 or below the excrescence formed by the junction with the host. 

 If the branch be cut off directly below the excrescence, new 

 growth of the parasite will not occur. A transverse section 

 through the base of the Loranth and Casuarina resembles a 

 wheel, the spokes of which are represented by the host, the 

 spaces between being occupied by the woody tissue of the 

 parasite (Pl.xviii., fig. 4). 



These nature-grafts differ one from the other in a marked 

 degree, being influenced by the nature of the host and the size of 

 the branch or twig on which the parasite first takes root. 



When a plant starts on a branch from 1-1 J inches in diameter, 

 the sinker penetrates the cortex and sapwood only (Pl.xix.fig.l). 

 The base of the attachment-disc becomes grafted to the surface 

 of the branch, and by the constant thrust exerted by the outward 

 growth of the base of the parasite, together with the irritation 

 of the cells, spreads the branch at right angles to its length 



