188 WwW. fT. GORDON 
In concluding this paper I desire to express my thanks to Dr Kripston, Dr Scorv, 
and Miss Benson, with whom I have been in constant communication during my work 
on the genus described here. I have also benefited greatly by a study of Dr Paun 
BERTRAND’S memoir on the Zygopteridean frond, and, although I cannot agree with 
all his conclusions, this work has been of great service to me. 
ee eS 
I have also to express my thanks to the Executive Committee of the Carnegie 
Trust for defraying the expenses of illustrating this paper. 
EXPLANATION OF PLATES. 
(Photographs from untouched negatives.) 
Unless otherwise stated, the sections figured are in the author’s collection. 
Puave I. 
Metaclepsydropsis duplex. 
Fig. 1. Transverse section of stem. «#!=outer xylem ; «?=pith with tracheides; p=parenchyma. Slide 
W129! x< 5288 
Fig. 2. Longitudinal section of stem. «#!=outer xylem; #?=inner xylem. Slide 1128. x 28. ; 
Fig. 3. Dichotomy of the stem, stage 1. a!=outer xylem; «?=inner xylem; rt. ¢r=root trace. Slide 
1120: sxl8: . 
Fig. 4. Dichotomy of stem, stage 2. Lettering as in last figure. Slide 1121. x 18. 
Fig. 5. Dichotomy of stem, section above fig. 4. «!=outer xylem; a?, ?=inner xylem. Slide 1122. 
x 18. 
Fig. 6. Dichotomy of stem just before the branches separate. Lettering as before. Slide 1123. x18. 
Fig. 7. Insertion of petiole-trace in stem. Petiole-trace detached. pra!, prx*=protoxylem groups; 
«} and «#? as before. Slide 1110. x18. 
Fig. 8. Insertion of petiole-trace in stem. Petiole-trace attached. «!=outer zone of xylem; 2?= inner 
zone ; prx', pr2? =protoxylem ; J =large xylem elements. Slide 1109. x18. 
Fig. 9. Stage below that of fig. 8. prx!, prx?=protoxylem groups. Slide 1108. x 18. 
Fig. 10. Section further in than fig. 9. prx!, prx?=protoxylem groups as before. Slide 1107. x 18, 
Fig. 11. Below fig. 10. a!=radial arm from inner xylem zone ; prx!, pra? =protoxylem groups. Slide 
LLOG... 18. 3 
Fig. 12. Stage preceding that of fig. 11. Lettering as before. Slide 1105. x18. 
Prats II. 
Metaclepsydropsis duplex. 
Fig. 13. Insertion of petiole-trace in stem. Stage below Pl. I. fig. 12. pra, prx? = protoxylem groups ; 
a =arm of parenchyma and tracheides radiating from inner xylem zone. Slide 1104. x 18. 
Fig. 14. Section following that of fig. 13. pra!=first protoxylem group. «!=sinus which is really 
the beginning of another radial arm similar to that of fig. 16. Slide 1103. x 18. 
Fig. 15. Section below that shown in fig. 14. pra! =first protoxylem group of petiole-trace ; a=radial 
arm of parenchyma and tracheides. Slide 1102. x 18. 
Fig. 16. Section below that shown in fig. 15. pra!=protoxylem groupi; a=arm of tracheides and 
parenchyma radiating from inner zone of stem axis. Slide 1101. x 18. 
Fig. 17. Transverse section of mature petiole-trace showing hour-glass shape. = waist; )=pinna-trace- 
bar; y=groove ; prx=protoxylem groups ; end=endodermis. Slide 1146. x17. 
