578 PARASITISM OF NOTOTHIXOS INCAXUS VAR. SUBAUREUS, 



Notothixos the position is slightly different, inasmuch as the eambial zone Joes 

 not extend in a continuous ring across the haustorium, for, in the central region, 

 continuous with the cambium, the cells are not actually meristematic ; nor is the 

 strand of haustorial tracheids severed. Conduction of liquids absorbed from the 

 wood of the host takes place through strands of tracheidal cells towards the main 

 sylem bundles of the mother root. In Text-fig. 7 it will be observed that the 

 cambium passes upwards towards the vascular tissue of the main root. 



Structures resembling laticiferous tissues occur in the haustorium (Text-fig. 

 7, l.t.). These contain a dense, granular, gumlike substance which stains a deep 

 reddish colour with safranin. Most of the parenchyma cells of the haustorium 

 contain at least one crystal of calcium oxalate. 



The haustorial cambium cuts off parenchymatous cells externally, so that 

 the phloem and cortex of the host-stem become more and more crushed and dis- 

 organised (Text-fig. 10). From this mass of cells at the base of the haustorium, 

 there grow out, in different directions, a series of branches. As the older haus- 

 torium gTadually encircles a considerable portion of the host-stem, by traversing 

 the bark and cambium and sending lateral projections of tissue into the wood, 

 the radiating branches formed from the haustorium, in the flux of time, come to 

 almost encircle the host-branch. In various species of Loranthus, knots of con- 

 siderable size are formed in the region penetrated by the haustorium, and from 

 them new branches and secondary roots are developed, spreading the parasite 

 over the host. In Notothixos the knots are small or frequently absent, and only 

 leafy branches are developed. As a consequence, Notothixos occurs isolated upon 

 the host, and no secondary roots bearing secondary haustoria and leafy shoots 

 are developed. 



The aerial branches show no definite relation to gTavity, since they grow 

 in all directions into space. They later bear the inflorescences. 



The haustorium, a small part of the primary root of the parasite, embedded 

 in the host, is therefore capable of the complete regeneration of the body of the 

 parasite, and develops branches, leaves and flowers. 



There seems no doubt that the primary haustorium of Notothixos is, from 

 the morphological standpoint, a portion of the primary root of the seedling; 

 the lateral projections of this haustorium are simply branches of this root. The 

 structure of the root, however, is radically altered to perform certain physio- 

 logical work for which the original root structure is unsuitable. 



The leaves of Notothixos have certain characteristic xerophytic features; they 

 are thick and fleshy; the stomata are slightly sunken. The lower surface is 

 covered with a dense growth of peculiar, branched, septate, golden-coloured hairs 

 (Text-flg. 11), which reduce transpiration. On the upper surface there are few 

 hairs. 



There are certain important facts in regard to the haustorium of Notothixos, 

 namely, (a) the absence of sieve-tubes, (b) the absence of sieve-plates between 

 the haustorial parenchyma and the phloem of the host, (c) the presence of 

 laticiferous-like tubes densely charged with nutritive matter, and (d) a large 

 amount of calcium oxalate crystals in the parenchymatous cells of the haustorium. 



The non-existence of sieve-tubes leads to the inference that the parasite 

 cannot tap the indiffusible proteids of the sieve-tubes of the host. The ordinary 

 parenchyma of the haustorium, however, is probably able to withdraw by osmotic 

 action the soluble and more readily diffusible foods of the host's phloem. Any 

 difference in osmotic equilibrium betAveen parnsitic and host-tissues at the point 



