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Transactions. 



sections of the plant and prothallus shown in fig. 66 it was clear that even 

 at this early stage the peculiar brown deposit referred to by other writers in 

 their studies of the mature rhizome of Tmesipteris and Psilotum is present in 

 its first beginnings in the innermost layer of cortical cells. The rhizome 

 and the aerial stem of the plant shown in fig. 5 were similar to each other 

 in their vascular structure, three or four xylem elements lying more or 

 less collateral with a group of phloem. The fungal element was present, 

 in the cortical cells of the rhizome but not of the aerial stem, and in 



Fig. 81. — Transverse section of stele of rhizome of young plant. X 160. 

 Fig. 82. — -Transverse section of stele of rhizome of medium-grown plant. X 125. 

 Fig. 83. — Transverse section of stele of large rhizome of plant shown in Plate I. X 125. 

 Fig. 84. — Transverse section of stele of aerial stem of young plant shown in fig. 85. 

 X 125. 



neither case was the brown deposit to be seen. The endodermis was 

 here not so clearly defined as in younger plants. A transverse section 

 of the rhizome of a slightly older plantlet is given in fig. 81, and shows 

 that here the single group of xylem elements is placed centrally in the 

 midst of the darkly-staining phloem, the metaxylem having been formed 

 centripetally. Immediately surrounding the phloem are one or two layers 

 of larger cells, probably to be identified as pericycle and endodermis, whilst 

 the cortex is slightly collenchymatous and its innermost layer shows 

 marked evidence of the brown deposit. The middle cortical zone contains 

 the mycorhizal coils, while the outer surface and the rhizoids had the 



