188 Scientific Proceedings^ Royal Dublin Society. 



contact are provided with large pits. These giant tubular cells very often form 

 straight or slightly curved linear series connecting one bundle with another, 

 starting in contact with or very close to the thin-walled sheath. So far as our 

 obsei'vations go, they never contain starch, but possess a readily seen proto- 

 plasmic lining, in which is embedded a single nucleus. Often several of these 

 tubular cells run along side by side through the loose cells of the parenchyma. 

 The walls of these adjacent tubes cohere together, and where they cohere are 

 marked with pits. 



Apparently quite distinct from these giant cells of the fundamental 

 parenchyma, but sometimes associated with them, are narrow tubular elements, 

 which traverse the intercellular spaces of the fundamental tissue. They have a 

 diameter of about 0004-0007 mm. and a length of about 010-015 mm., and form 

 very long linear series originating from the bundles. They pass out from the 

 bundles into the cortical tissues, or penetrate through the inner tissues of the 

 haustorium. Each member of the series has a nucleus. Figs. 10, 11, PL IX, 

 show a sheaf of these elements which has branched in the cortical region, and has 

 sent one branch outwards through the cortex to the epidermis and another into 

 the deeper tissues of the haustorium. The whole length of this tract was about 

 2 mm. Fig. 11 shows the inner end of this tract more highly magnified. When 

 these tubular elements reach the outer tissues of the cortex, where the inter- 

 cellular spaces are injected with the debris of the endosperm, their ends enlarge 

 (figs. 12, 13, PI. X), and sometimes they push their way between the epidermal 

 cells and come directly in touch with the food supply (fig. 14, PL X). Sometimes 

 one finds their ends in intercellular spaces still within the tissue. In this case 

 they have a rounded termination, reminding one of the tip of a root-hair or a 

 rhizoid. 



The connexion of these tubular elements with the bundles may be seen in a 

 section cutting a bundle at right angles, just at the point where these tubules 

 emerge from it (fig. 5, PL VII). Here the tubules may be seen as continuations 

 of the groups composed of two, three, or more small angular elements, which are 

 scattered like small islands in the phloem and in the xylem-parenchyma. 



Fig. 9 is a tangential section of a bundle in the haustorium, and shows the 

 transverse section of a group of these tubules emerging through the bundle- 

 sheath. Fig. 8 is a transverse section of such a sheaf of tubules as it passes 

 across the fundamental tissue. It also shows the tubules running in an inter- 

 cellular space. 



The giant cells and the tubules seem often to accompany one another, but 

 they also occur quite separated from one another. 



The tubular form of both kinds of elements and the distance of the transverse 

 partitions in them from one another suggest that in them diffusion, or possibly 

 some other means of translocation, will take place less hampered than in the 

 isodiametrical parenchyma. 



From a causal point of view one is tempted to surmise that the exceptional 

 abundance of organic supplies has led to a hjijcrtrophy of two different cell- 

 categories to form rhizoid-like internal organs. 



On entering the haustorium, most of the bundles bend appropriately to 

 distribute themselves in the layers of fundamental tissue immediately next the 

 surface. In this region they bifurcate and anastomose to form a network, the 

 meshes of which are about i mm. or less across. Very often these bundles lie 

 immediately beneath the grooves separating the papillae of the haustorium 

 from one another, and from these bundles many of the tubular cells just described 

 extend into the tissues of the adjacent papillae, and running along immediately 

 beneath the epidermis, emerge at the surface between the epidermal cells (fig. 14, 

 PL X). Some bundles do not turn outwards towards the surface, but after 



