BY J. JICLUCKIE. 577 



the cells of the baustorium, and I am convinced that no such structural 

 provision is made in order that the most important proteids may enter the haus- 

 torium. Structural evidence points to the conclusion that Notothixos is a water- 

 parasite, tapping only the vessels of the host. 



Pierce (1905) did not find any sieve-plates between the sieve-tubes of the 

 Pine, and the baustorial cells of Arceuthobium occidentale, or in the other 

 chlorophyll-bearing parasites, Visciim and Phoradendron, but he points out that, 

 for a part of its life history, Arceuthobium is represented only by a mass of 

 baustorial tissue embedded and concealed in the host. This paxt is devoid of 

 chlorophyll. When activity is re-awakened in the spring, and new buds are 

 developing into branches bearing leaves, it must be either at the expense of the 

 reserve foods stored in the parenchymatous tissues of the baustorium, or in 

 those of the host, or at the expense of foods withdrawn from the phloem of the 

 host, or probably both sources are drawn upon. Pierce came to the conclusion 

 that Arceuthobium, on account of its peculiar periodic life-history, was a more 

 complete parasite than Viscum and Phoradendron. The penetrating part of 

 Arceuthobium is probably completely parasitic, while it is free of aerial chloro- 

 phylliferous branches. 



Benson (1910), in Exocarpus, found cytoplasm and food granules in the 

 tracheids of the root-haustoria, and expresses the opinion that they function in 

 the collection and conduction of soluble substances from the host-cells, since a 

 tj^ieal phloem is reputed to be absent from the baustorium of the root-parasites 

 described. In other words they combine the structure and function of phloem 

 and sylem elements and are referred to as "Phloeotracheids." 



With Notothixos the matter appears to be different. This is an evergreen 

 form which shows considerable physiological activity prior to and during re- 

 production and then, after the maturation of the fruits, lapses into a phase of 

 comparative inactivity. During this period considerable masses of starch grains 

 are present in the pai-encbymatous cells of the baustorium and, when physiological 

 work begins again, culminating in reproduction, it is apparently at the cost of 

 these reserves. There is not the same necessity as in Arceuthobium for a with- 

 drawal of food from the host-tissues. Even in times of great stringency the 

 parasite does not seem capable of obtaining sufficient nutriment from the host 

 to preserve itself. Notothixos and Loranthus frecjuently kill the end of the host 

 branches by depriving them of water; but they frequently perish too. It seems 

 to me that, were these parasites in the habit of extracting food from the host, 

 they would be able to preserve themselves in times of stringency when their own 

 leafy branches are dying. There is some evidence that the tracheids of the 

 baustorium of Notothixos perform the dual function of phloem and xylem 

 elements. 



During the development of the' baustorium, the cambial ring of the host- 

 stem is interrupted, but in old haustoria this cambial ring is again practically 

 completed by the formation of a cambial zone in the basal region of the baus- 

 torium itself. From this baustorial cambium, more or less radial rows of 

 parenchymatous cells are cut off internally; many of these become transformed 

 into the typical thick, reticulate-walled tracheids (Text-flgs. 7, 10). 



The reorganisation of a practically complete cambial ring in Notothixos 

 recalls the similar feature of the baustorium of Visciim album which Pierce (1S93) 

 has already described. In this case the strand of tracheids in the baustorium is 

 completely severed by a layer of compact, small, meristematic cells, so that the 

 solutions extracted from the xylem of the host must pass through these cells In 



