of Goal-Measure Plants. 143 



branching ; there are two circular steles, apparently equal in size, 

 enclosed in a common mass of ground-tissue ; one of them is well 

 preserved (Text-figure 1), but the other has been considerably 

 crushed. The main mass of the ground-tissue consists of paren- 

 chyma, which may be spoken of as the middle cortex, and scattered 

 through this tissue several leaf-traces are seen in slightly oblique 

 transverse section. Near the periphery of the section there is an 

 irregular line of tearing, represented by a light-coloured band 

 occupied by the mineral matrix; this line is situated just external 

 to the outer limit of the middle and the inner margin of the more 

 compact outer cortex. The surface of the whole section does not 

 correspond exactly with the original surface of the stem, which had 

 lost its superficial tissues previous to petrifaction. At the level at 

 which the section was cut, the elliptical and flattened form of the 

 stem marked the approaching division into two equal branches ; 

 internally the occurrence of two separate steles and the bending 

 inwards of the outer cortex between the vascular cylinders show 

 that the branches must have become free from one another at a 

 short distance above the region represented by the section. 



Figure 1. Transverse Section of one of the Steles shown in Slide 1. 



(xlO.) 



The dark irregular boundary of the primary xylem is clearly shown ; 2 mm. 

 external to this, as measured on the photograph, the lighter tissue with large 

 clear spaces represents the " secretory" zone. [This stele is figured by Binney 

 (71) in his PL vn. fig. 6.] 



11—2 



