THE STRUCTURE AND AFFINITIES OF DIPLOLABIS ROMERI (SOLMS). 735 



Fig. 20. Petiolar departure, petiole-trace free from stem-xylem. x., x., 1 and prx., as before, x 1P6. 

 (Slide 742.) 



Fig. 21. Petiole-trace — transverse section — while still in cortex of stem. Each protoxylem has divided 

 into two. prx. v prx.-^ 1 , }>rx. 2 , prx. 2 1 = -ptotoxylems. x 7'5. (Slide 336.) 



Fig. 22. Transverse section of petiole-trace similar to that of fig. 21, but slightly further out. It is still, 

 however, in the stem-cortex. Lettering as before, x 10. (Slide 285.) 



Fig. 23. Transverse section of petiole-trace beyond fig. 22. t. = tongue of xylem ; is., is. = island of paren- 

 chyma; d. = departing trace (root?). x 10. (Slide 343.) 



Fig. 24. Section following fig. 23. t. = tongue of xylem; is., is. = island of parenchyma. x 11. (Slide 

 344.) 



Fig. 25. Stage after fig. 24. b. = xylem-bar (the united traces of two reduced pinnae) ; is., is. =islands of 

 parenchyma, one large one at top and two small ones at lower end. x 11. (Slide 348.) 



Fig. 26. Stage following fig. 25. prx. = protoxylems. Arms are now distinct. x 10. (Slide 284E.) 



Fig. 27. Stage beyond that of fig. 26. prx. = protoxylem ; p. v p. 2 = united traces of a pair of reduced pinnae ; 

 the traces are connected together by a thread of xylem. x 7. (Slide 719.) 



Fig. 28. Stage above fig. 27. Trace similar to that of Diplolabis forensis Renault, prx. = protoxylem. 

 x 7. (Slide 726.) 



Fig. 29. Stage following that of fig. 28. This is the normal Diplolabis romeri trace, prx. = protoxylem. 

 x 7. (Slide 699.) 



Plate III. 

 Diplolabis romeri. 

 Series of photomicrographs illustrating the changes in the petiole-trace. 

 Fig. 30. One end of a transverse section of peliole-trace above stage of PI. II. fig. 22. is. = island of 



parenchyma. x 25. (Slide 341.) 



Fig. 31. Section above fig. 30, same end of trace, t. = tongue of xylem; prx. = protoxylem. x 25. 



(Slide 342.) 



Fig. 32. Next section above fig. 31. t. = tongue of xylem; d. = departing trace (root?). x 25. 



(Slide 343.) 



Fig. 33. Section above fig. 32. Note tridentate end of trace. x 22. (Slide 344.) 



Fig. 34. Following fig. 33. Arms closing over to unite with xylem tongue. X 25. (Slide 345.) 



Fig. 35. Section following fig. 34. Arms united with tongue of xylem. Two islands. x 25. 



(Slide 346.) 



Fig. 36. Stage after fig. 35. The two islands of parenchyma are very distinct. x 25. (Slide 347.) 

 Fig. 37. Trace beyond stage of fig. 36. is., is. =the two islands of parenchyma. x 25. (Slide 348.) 

 Fig. 38. Section above that shown in fig. 37. is., is. = islands of parenchyma. x 25. (Slide 349.) 

 Fig. 39. Stage after fig. 38. is., is. =islands of parenchyma. x 25. (Slide 350.) 

 Fig. 40. Two sections above fig. 39. The two islands have united into one. c, c = two ends of reniform 



island of parenchyma. x 25. (Slide 352.) 



Fig. 41. Trace of fig. 33, other end of trace, to illustrate the difference in phase of the two ends of the 



same trace. x 22. (Slide 344.) 



Plate IV. 

 Diplolabis romeri. 



Fig. 42. Transverse section of normal Diplolabis romeri petiole-trace, a., a. = lines of abscission of pinna- 

 trace-bar ; b = pinna-trace-bar ; c, c = claw-like ends developed from the arms. They ultimately join and 

 form the next pinna-trace-bar. x ! 4. (Slide 793.) 



Fig. 43. Transverse section of petiole showing the division of the pinna-trace-bar. pin. tr. = pinna-trace ; 

 aph. tr. = aphlebia-trace ; o. c. = outer cortex. x 2 4. (Slide 789.) 



Fig. 44. Transverse section of petiole showing bifurcation of aphlebia-trace. pin. tr. = pinna-trace ; 

 aph. tr. = aphlebia-trace (four of them), x 2-2. (Slide 796.) 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART IV. (NO. 24). 108 



