210 MR R. J. D. GRAHAM ON 



they never interfere with the average number of bundles, and hence the type can 

 always be determined. Two other important features for distinction of species are 

 mentioned by Fritsch (ll). These are the occurrence of isolated groups of 

 sclerenchyma in pith and cortex, and the distribution of secretory organs. Both of 

 these can be applied to the genus Ephedra. The development of the mesocortical 

 stereom web, as already mentioned, is much better in some species than in others. A 

 division can, therefore, be made into species which have a well-developed mesocortical 

 stereom {foliata, distachya, viridis), and those in which the stereom is poorly developed 

 {trifurca, fragilis, Helvetica, procera). Again, the extent to which the perimedullary 

 stereom is developed furnishes a basis for another threefold division. The perimedullary 

 stereom is represented in two stages of development — as a discontinuous ring (nebro- 

 densis), as a series of isolated fibres {trifurca, foliata, distachya, viridis), or as absent 

 altogether {fragilis, Helvetica, gerardiana, procera). The presence of tannin sacs in the 

 pith of many species {Helvetica, distachya, procera) furnishes another basis for division. 

 In determining the value of varieties, histology plays an important part. Thus 

 E. nebrodensis differs from E. procera, not only in the former having a roughened 

 epidermis while the latter is smooth, but E. nebrodensis has ten vascular bundles, while 

 E. procera has only eight. A striking instance occurred in regard to three specimens 

 received from Edinburgh. The names borne by the plants were apparently synonyms 

 for E. altissima. Their identity was established by a study of their histology, and by 

 a subsequent examination of the plants with regard to external morphology the 

 identity was confirmed. 



TABLE OF SPECIFIC DISTINCTIONS, BASED ON THE CHARACTER OF THE VASCULAR 

 SYSTEM OF THE SECOND INTER NODE, STEREOM GROUPS, AND PITH. 



1. E. trifurca (Torb). Primary bundles, 12 or 15. Mesocortical stereom web poorly developed. 



Perimedullary stereom isolated fibres. No pith tannin sacs. 



2. E. foliata (C. A. Meyer). Primary bundles, 8. Mesocortical stereom web well developed. Peri- 



medullary stereom isolated fibres. 



3. E. fragilis (Desf.). Primary bundles, 8. Mesocortical web poorly developed. Perimedullary 



stereom absent. No pith tannin sacs. 



4. E. Helvetica (C. A. Meyer). Primary bundles, 8. Mesocortical stereom web poorly developed. 



Perimedullary stereom absent. Pith tannin sacs. 



5. E. distachya (Lin.). Primary bundles, 8. Mesocortical stereom web well developed. Peri- 



medullary stereom isolated fibres. Pith tannin sacs. 



6. E. gerardiana (Wall). Primary bundles, 10. Perimedullary stereom absent. Pith tannin sacs. 



7. E. nebrodensis (Tineo). Primary bundles, 10 or 15. Perimedullary stereom discontinuous ring. 



No pith tannin sacs. 



8. E. procera (C. A. Meyer). Primary bundles, 8. Mesocortical stereom web poorly developed. 



Perimedullary stereom absent. No pith tannin sacs. 



9. E. viridis (Coville). Primary bundles, 10. Mesocortical stereom web well developed. Peri- 



medullary stereom isolated fibres. Pith tannin sacs. 



In conclusion, I wish to thank Mr R. A. Robertson, at whose suggestion the work 

 was undertaken, for his great help throughout its course. 



