THE ANATOMY AND AFFINITY OF DEPARIA MOOREI, HOOK. 845 



and a region follows in which the trace possesses at one point four, at another point 

 three, strands. Towards the top of the rachis the trace is uniformly composed of 

 three strands (fig. 5), and this condition is maintained to the point of departure of 

 the pinnae. 



In illustration of the relative proportions of the rachis in which the various 

 numbers of leaf-trace bundles were found, it may be stated that out of a total of 

 805 sections of fairly uniform thickness into which a rachis was cut, 298 possessed 

 three strands, 335 had four, 166 had five, while only 6 had six. 



The histological details of the large adaxial bundles are — as seen in transverse 

 section — fairly constant, but in this respect the small abaxial strands are naturally 

 more variable. In the leaf-base an adaxial strand consists of an elliptical mass of 

 tracheides surrounded by a narrow even zone of phloem. Both the pericycle and 

 endodermis are one cell broad, and the inner and lateral walls of the latter are 

 especially thickened. At this level the details of the small abaxial strands are 

 usually reproductions in miniature of the arrangement just mentioned. The pro- 

 toxylems are seldom distinctly marked. 



Throughout the greater part of the rachis, however, while the general elliptical 

 form is maintained by each adaxial strand, the xylem is more attenuated in section, 

 appearing as a slightly curved mass usually possessing a protoxylem group at each 

 end, but having the bulk of its metaxyiem collected towards the abaxial end of the 

 bundle (figs. 9-5). The phloem is a broad, small-celled zone, almost or completely 

 enclosing the xylem and surrounded by a pericycle which consists of two large-celled 

 rows on the upper side of the bundle, but increased to four or five rows on the lower 

 side. The endodermis is as in the leaf-base, but thin-walled passage cells are 

 abundant opposite the more adaxially situated protoxylems. Apart from the variety 

 in form and size, the scarcity of passage cells in the endodermis, and the uniform 

 thickness of the pericycle, nothing need be mentioned regarding the abaxial strands. 



The foregoing account of the anatomy of the rachis will suffice to show that the 

 leaf-trace is of an advanced type, and that, when followed from the leaf-base to 

 the point of departure of the pinna-traces, it is found to undergo considerable 

 reduction. 



Anatomy of the Pinna-Traces. 



The rachis divides into three primary pinnae. One is the median upward con- 

 tinuation of the rachis, the other two are lateral and project abruptly to the right 

 and left respectively. The lateral pinnae do not depart at exactly the same level, 

 but one stands slightly above the other. This is not without its bearing on the 

 mode of separation of the pinna-traces from the three bundles of the rachis. Slight 

 differences in detail from the following account were observed in some of the leaves 

 examined, but those were only minor differences, and their existence alone need 



be noted. 



TRANS. ROY. SOC. EDIN., VOL. L, PART IV (NO. 26). 121 



