0'4 PARASITISII OF NOTOTHIXOS INCANUS VAR. SUBAUEEUSj 



(Text-fig. 3). The growth of the root is stopped by some roughness or obstacle 

 in the direction of its growth; when a resistance is provided the root forms a 

 small club-shaped holdfast. In the absence of contact with a resisting body the 

 holdfast is not developed (Text-fig. 4). 



Primarily the holdfast consists of an undifferentiated mass of actively meris- 

 tematic cells, but the dermatogen cells in contact with the obstacle elongate con- 

 siderably and securely attach the holdfast. These elongated cells recall the 

 "cushion cells" of the haustoria of Cuscuta (Pierce, 1893). The holdfast grows 

 as the food is transported from the endosperm. The central region of the hold- 

 fast undergoes differentiation, and a mass of tissue gTOws out from it into the 

 bark of the branch. Penetration is probably dependent upon a certain amount 

 of pressure, but mainly upon chemical solution. There is very little indication 

 of a pressure-effect in the direction of growth of the haustorium, although, in 

 the mature haustorium, the phloem and cortex along the margin of the sucker are 

 crushed. The mechanical conditions for the development of pressure by the 

 haustorium are not so efficient as in Cuscuta. Evidences of chemical action are 

 numerous, namely, discolouration of the host-tissues in front of the haustorium, 

 and the pushmg inwards of the walls of the host by the penetrating epidennal 

 cells of the sucker (Text-figs. 5, 6), and the very exact application of the 

 tracheids of the haustorium to the vessels of the host. The epidermal cells of the 

 tip of the haustorium are slightly papillate, fairly long and have dense cyto- 

 plasm and a large nucleus. Immediately behind this layer the cells are small and 

 meristematic. The penetration of the haustorium leads to the destruction of a 

 considerable wedge of cortex, phloem, cambium, and part of the wood of the 

 host. When the haustorial tissue taps a number of vessels of the host branch, 

 certain cells of the peripheral layer differentiate into short reticulate tracheids 

 which link up with others already formed in the central shaft of the sucker. 



Text-fig. 1. A longitudinal section of the fruit, showing epidermis (ep.), fruit- 

 coat (f.c), gelatinous layer (g.l.), the tracheid-bearing layer (tr.l.), 

 endosperm (end.), embryo (embj, stigma (st.), dehiscent zone 

 (deh.). (x 10). 



Text-fig. 2. Cell from gelatinous layer, showing gelatinous layer (g.l.), and 

 spirally thickened cellulose layer (c.l.). (x 125). 



Text-fig. 3. Seedlings of Notothixos showing curvatures of the root and hpyo- 

 cotyl. (slightly enlarged). 



Text-fig. 4. Holdfast developed from the root-apex when resistance to growth is 

 provided, (slightly enlarged). 



Text-figs. 5, 6. Portion of haustorium (H) in contact with the vessels of the 

 host. The papillate character of the peripheral layer is shown, while 

 some of the cells have pushed in the walls of the host-cells (v.h.). 

 (x 110). 



Text-fig. 7. L.S. of mature haustorium embedded in the xylem of the host; 

 laticiferous tissues (l.t.), cambial zone (c.l.), phloem (p.h.), cork (c.) 

 are shown, (x 50) . 



Text-fig- S. Longitudinal section through host and haustorium showing relation 

 of parasite to the host vessels, (x 125). 



Text-fig. 9. Application of a haustorial tracheid to a vessel of the host, (x 125). 



Text-fig. 10. Part of the central zone of the haustorium (c.) with the crushed 

 phloem (ph.) of the host, (x 125). 



Text-fig. 11. Lower epidermis of leaf showing one of the septate hairs, (x 125). 



