Dixon and Ball — Channels of Transport in Seedlings. 193 



6. Material produced by the disintegrated endosperm finds its waj^ into the 

 outer interceHular spaces of the haustorium of Lodoicea sechellarmn, passing- 

 between the epidermal cells. 



7. Tubular cells taking their origin at or near the sheath of the vascular 

 bundles of the haustorium of Lodoicea sechellnrum pass between the isodia- 

 metrical cells of its spongy tissue. They form connexions with these cells, and 

 their walls are pitted at the points of contact. They often form connexions 

 between the sheaths of the vacsular bundles. 



8. Cxroups of narrow tubular elements are found in the phloem and xylem of 

 the bundles of the haustorium of Lodoicea. Here and there sheaves of these 

 pass out of the bundles into the intercellular spaces of the surrounding tissues. 

 Sometimes they turn inwards and push their way among the cells of the central 

 fundamental tissue; more frequently they turn outwards and ti-averse the 

 cortical region. When they come immediately beneath the epidermis, their 

 ends expand, and may e-\-en push out between the epidermal cells to the surface. 



Conclusions. 



1. The presence of the vascular uetworlc in haustoria and of conducting tracts 

 in the transmitting organs suggests that the vascular bundles are the channels 

 by which the embryo receives the organic sirpplies from its storage organs. 



2. The development of tracheal tubes in transmitting organs of seedlings, 

 where the transport of water is unnecessary, is in confonnity with the view that 

 these tubes convey organic store material. 



3. Experiment shows that these tubes will convey fluid either in a basal or 

 in a distal direction, according to the position of the source and sink. 



4. The lateness in the differentiation of the sieve-tubes in the vascular 

 strands of the petioles of the cotyledons of Vicia faba shows that much transport 

 of organic substance down the petiole is effected without their assistance. During 

 this jieriod tracheae are available. 



5. Transport of organic substance through the parenehjTnatous cells of the 

 haustoria and through those of storage cotyledons has to be attributed to the 

 permeability of the protoplasm of these cells. It seems gratuitous to assume 

 that the cells adjacent to the tracheae are the only cells in these organs which 

 are impermeable. If they are permeable, the tension set up in the tracheae will 

 secure movement of organic fluids into and along the tracheae. 



6. The great development of the phloem in the haustoria compared with its 

 mass in the transmitting organ — the petiole — suggests that this tissue is chiefly 

 concerned with the preparation of the organic substance absorbed and its trans- 

 mission into the tracheae. 



7. It may be pointed out that sieve-tubes in their mature state are by no 

 means ideally constructed for the transmission of organic substances. The 

 pores in their sieve-plates are exceedingly fine, aird they are mostly or entirely 

 blocked by protoplasm or callus. Bearing in mind the semi-permeable nature of 

 protoplasm, it would appear that the sieve-plate would present a greater obstacle 

 to the flow of most solutions and every sol than would a simple cell-wall. It 

 seems quite possible that we should regard the sieve-tubes rather as minute 

 reservoirs than as conduits. 



8. The contrast of appearance of the phloem-parenchyma (cambifonn cells) 

 in this connexion is suggestive. The bundle endings in leaves and in growing 

 points, as is well known, are without well-differentiated sieve-tubes, and their 

 phloem is composed of cambifonn cells onl.y. These may be supposed to be 

 effective in transmitting the products of photosj'nthesis into the tracheae and at 

 the growing points to extract these supplies for the growth there. 



SCIENT. Pr.OC. K.D.S., VOL. XVII, NO. 21. 2 M 



