844 MR JOHN M'LEAN THOMPSON ON 



marking the positions of a succession of points at which necks of thin-walled tissue 

 traverse the peripheral sclerotic zone and establish connections between the central 

 ground-parenchyma and the epidermis. At those points the epidermal cells are 

 thin-walled, and occasionally a stoma is formed. These lateral lines mark the 

 positions of two chains of lenticels. 



The details of the number of bundles in the leaf-trace and of the course which 

 they follow once they have entered the leaf-base are very variable. It has already 

 been stated that a leaf-trace which consists of three bundles when it leaves the 

 leaf-gap, may be possessed of four or five strands before it passes into the leaf-base. 

 In no case was a sturdy leaf-base found to possess less than four leaf-trace bundles. 



This at least is constant. The two largest bundles in the trace have sprung one 

 from each side of the leaf-gap, seldom close to its summit and often near its middle. 

 At no point in their passage through the cortex are they united by commissural 

 strands, and when they enter the leaf-base they take up adaxial positions at a good 

 distance apart, and — as seen in transverse section (fig. 10) — slant towards each other 

 so that if their long axes were produced they would meet to enclose a right angle. 

 Throughout the entire length of the rachis they retain their adaxial positions, and 

 maintain their independence of each other. 



The remaining two or three bundles of the trace enter the leaf-base towards its 

 abaxial side. They are invariably smaller than the adaxial strands, and vary in size 

 among themselves. From point to point on their way through the leaf-base into 

 the rachis their relative positions change. At one point two bundles suddenly 

 approach each other and establish a connection by a short, thin commissure, or 

 become fused for a little distance. At other levels a short strand locally unites a 

 small abaxial bundle to the nearest corner of one of the large adaxial strands, or a 

 narrow bundle passes from an adaxial strand and gradually approaches and finally 

 unites with an abaxial strand. 



The lowest portion of the rachis is, in fact, marked by sudden and varied 

 anastomosings mainly involving the small abaxial bundles, and thus the leaf-trace 

 which at one point consists of five strands may suddenly reduce to four. It may 

 then increase as suddenly to six, only to be again reduced to five (figs. 10-7). The 

 dominant number of strands in the short basal part of the rachis is five, six strands 

 being established only very locally. Higher in the rachis the changes in number and 

 disposition of the bundles are fewer and less sudden, and, as a rule, the small abaxial 

 strands alone are involved in the anastomosings. From thence upwards for some 

 distance the bundles fluctuate from four to five in number, but at length settle down 

 to be a group of four, consisting of two very similar large adaxial and two unequal 

 abaxial strands (fig. 6). In this region the larger abaxial bundle always tends to lie 

 in a position about equidistant from the adaxial strands, while its smaller neighbour 

 is more lateral. At length a junction is made between the abaxial strands and the 

 trace is reduced to three bundles. Four strands are, however, again established, 



