226 ME R. KIDSTON AND MR D. T. GW YNNE-A r AXJGHAN ON 



with roots. The xylem strands of the roots are inserted upon the sides of those of the 

 leaf-traces just as the latter separate from the xylem of the stem (fig. 18, r. st.). The 

 roots run more or less horizontally through the cortex, taking a sinuous course and 

 turning aside from time to time to avoid a leaf-trace or another root. 



When about half-way through the inner cortex of the stem they obtain a cortex of 

 their own, which consists for the most part of very thick-walled fibrous sclerenchyma 

 (fig. 19, se. v.). The cells are smallest and thickest at the outside ; towards within they 

 increase in size, while their walls diminish in thickness. The last one or two layers next the 

 endodermis are comparatively thin-walled. The cells of the endodermis are tangentially 

 elongated and filled with brown, densely granular contents (fig. 20, tn.). It probably 

 consists of a single layer of cells, but it is difficult to make sure of this, for the adjacent 

 cells sometimes contain an exactly similar substance. 



The xylem strand is diarch and oval, with a few very small protoxylem elements at 

 the two ends. The xylem is surrounded by a parenchymatous sheath two or three cells 

 thick, and this is followed by the phloem, which is in considerable quantity on the sides 

 of the xylem. It is possible also to distinguish protophloem on the outside of the two 

 phloem groups (fig. 20, pr. ph.). The phloem is separated from the endodermis by two 

 or three layers of pericycle similar to that of the stem in general appearance. 



Locality. — Mine Kluczersky, district of Bjelebei, government of Orenburg, Russia. 



Horizon. — Upper Permian (P2 of Geological Table, p. 219). Specimen preserved 

 in the Museum of the Institute of Mines, St Petersburg. 



Zalesskya diploxylon, Kidston and Grwynne-Vaughan, n.sp. 



(PL IV. figs. 21-28.) 



The general appearance of this fossil suggests that it has undergone a considerable 

 amount of change after mineralisation, owing to the percolation of water through the 

 stone. The sections were of a light fawn colour, much of the carbonaceous matter 

 originally present having been removed. However, a certain amount of this has been 

 redeposited in the form of minute granules, flakes, and specks, and in some parts 

 of the fossil as large irregular aggregations. The substance of the fossil as it exists at 

 present is very porose and friable. 



The transverse section of the specimen is circular, with a diameter of about 3*5 cm. 

 (fig. 22). There is a fairly large stele measuring 7 mm. across. The greater part of the 

 xylem is still preserved, but unfortunately the more central elements of the stele have 

 crumbled away, owing to the friable nature of the fossil. The xylem is surrounded by 

 a rather conspicuous ring of phloem, visible to the naked eye, and this in turn by a 

 very wide cortex entirely composed of thin-walled parenchyma. In our specimen the 

 whole of the outer part of the stem, and also the mantle of persistent leaf-bases that 

 probably coated the stem proper in the living plant, have; not been preserved. It 

 follows, therefore, that the surface of the fossil as shown in fig. 21 represents a 



