164 Mr Seward, Notes on the Binney Collection 



distinguished. As already pointed out there are approximately 30 

 groups of protoxylem distinguishable in the peripheral region of 

 the primary xylem of a complete transverse section {e.g. PL VI.); 

 this number is in agreement with the approximate estimate of six 

 protoxylem groups in each leaf-trace. The oval group of tissue, 

 It, of fig. 5, PL v. projects slightly into the secondary wood, and 

 represents a leaf-trace on the point of passing through the 

 secondary vascular tissues on its way to the surface of the stem. 

 The tracheids of a leaf-trace such as that seen in transverse 

 section in figs. 2 and 5, PL v., and at It 1, PL VI., appear 

 in longitudinal view as long reticulately pitted tracheids of 

 the ordinary type, associated with xylem parenchyma (It text- 

 figure 2). 



Returning to fig. 7, PL VI. we notice two other regions in the 

 peripheral part of the primary stele which are occupied by narrow 

 tracheids, It 2 and It 3, but these constitute less compact groups 

 than It 1 of the same section, and spread over a greater area, at 

 the edges of which they merge into the larger tracheal tissue of 

 the metaxylem. The group It 2 in fig. 7 (PL vi.), shown more 

 clearly in figs. 3 and 6, PL v., is much less compact and sharply 

 limited than the group It 1, but more compact than It 3 of fig. 7, 

 PL VI. Both groups It 2 and It 3 are leaf-traces cut through at a 

 different level from that of It 1. In addition to the traces It 2 

 and It 3 of fig. 7, there are distinct indications in other parts of 

 the periphery of the primary stele of the same section of 

 portions of two more such groups, in the form of strands of 

 narrower tracheids with protoxylem elements more widely 

 separated from one another in a lateral (or tangential) direction 

 than the protoxylem exarch strands of the leaf-traces It 1 — It 3. 

 One of these more widely separated groups of leaf-trace tissue is 

 situated a short distance to the right of It 1 of fig. 7, PL VI.; this 

 we may designate It 4, and the other, which is still less clearly 

 defined — the leaf-trace tracheids and parenchyma being spread 

 over a greater area — occurs slightly to the left of It 2, and may be 

 spoken of as It 5. Fig. 8, PL VII. shows some of the peripheral 

 protoxylem strands of a leaf-trace as seen in a lower part of its 

 course than in the section represented in PL V. fig. 3 ; in fig. 8 

 the protoxylem strands are farther apart tangentially, and this is 

 the result of the lateral spreading of the trace in the deeper part 

 of its course. 



The disposition of the leaf-traces with their protoxylem 

 strands, as seen in transverse section, agrees with a phyllotaxis of 

 tw T o-fifths. The size and degree of compactness of the leaf-trace 

 groups afford guides as to the relative levels at which the section 

 has intersected the leaf-traces, the more compact the foliar vascular 

 strands the higher they are in their upward course. The transverse 



