Dixon and Ball — Channels of Transport in Seedlings. 189 



entering from tlie petiole sti'ike across tire central tissue of the haustorium, and 

 make connexion with the network formed by the others at the distal surface of 

 the haustorium. 



On leaving the petiole, the bundles soon lose their selerenchjTnatous sheath, 

 and are continued as a double strand of xjdem and phloem, surrounded by an ill- 

 defined sheath of elongated, prismatic, thin-walled cells (fig. 6, PI. VIII). On 

 the outside these adjoin the spongy parenchyma. Within the sheath the phloem 

 is composed of sieve-tubes, companion-cells, and bast-parenchyma. The latter 

 occupies the greater part of the phloem. Its cells are comparatively large, 

 having a diameter of 002-003 mm., and being 010-0-20 mm. in length. The 

 sieve-tubes and companion-cells are in small groups, and associated with them 

 are the groups of tubular elements already noted, among the phloem-parenchyma. 

 The whole cross-section of the phloem contains about 120 elements. In the 

 cross-section of the xylem, on the other hand, 12-18 elements are seen. They are 

 spiral and annular tracheae and xylem-parenchj-ma and one or two groups of 

 the tubules. The ratio of the cross-section of the phloem to that of the xylem 

 in the bundles of the haustorium is about 8 : 1, which is a marked contrast to 

 the same ratio in the petiole, which is 30 : 2-5 (cf. figs. 6 and 7, PI. VIII). 



The haustorium of the specimen we examined was embedded in the softened 

 tissue of the endosperm. This was in turn surrounded by the outer layers of the 

 endosperm which were still white, and of stony consistency. The inner layers 

 next the haustorium were yellowish and pasty, and. could be scooped out with a 

 spoon. Both the soft and hard laj'ers gave a blue reaction with iodine and 

 sulphuric acid, and the soft part reduced Benedict's solution after standing 

 some days with toluene (cf. 9, 10). 



Microscopic examination showed that in the pasty substance cell-structure 

 was more or less obliterated. The wall-substance was jellified and the proto- 

 plasm indistinguishable. The hard tissue was still composed of very thick- 

 walled prismatic cells, arranged perpendicularly to the surface of the seed. 

 Their ends were bevelled. In the comparatively small lumen there was visible 

 a distinct lining of cytoplasm, in which was a nucleus. The vacuole contained 

 varying quantities of mucilage. Deep and wide pits extended into the secondary 

 layers of wall-substance to the limiting membrane of the end and side walls 

 (compare Gardiner's fig. 20, in 7). The outer diameter of the endosperm cells 

 ranged from 009-013 mm. The diameter of the lumen was 008-003 mm. The 

 lengths of the cells varied from 040 mm. to 120 mm. 



PJicenix dactylif era. 



The general course of the germination of Phcenix dactylif era is well known 

 (8, 11, 12). 



There are about eight or nine bundles in the cross-section of the petiole of the 

 cotyledon. Most of these bifurcate before entering the haustorium, so that 

 there are about sixteen at the level of the constriction' below the haustorium 

 (fig. 17). On entex'ing the haustorium they diverge from one another, and run 

 along just under its convex surface towards its margin. The haustorium itself 

 is in the early stag'e button-shaped — oval in outline and slightly concave on its 

 distal aspect. Pigs. 16 and 17, PL XI, show the distal and proximal surfaces of 

 the haustorium of an embryo just emerging from the seed. Just below the 

 margin the bundles branch again, so as to give rise to 35-40 bundles which turn 

 over the margin, converge, anastomose irregularly, and closely follow the concave 

 surface towards the middle of the haustorium. Thus, close beneath the surface 

 of the haustorium there is a network of vascular bundles, connected by about 

 16-20 main bundles with the vascular system of the petiole, and ultimately with 



