14 Transactions. 



Conclusion. 



The study of the structure of the few tree-ferns examined, 

 and their comparison with other forms, makes me feel that the 

 form of the stele is too directly adaptive to prove relationship. 

 Among the modern ferns the function of the stem decides 

 the form of stele. If the stem is a creeping one, and not too 

 bulky, then a tubular stele is found — c/. some species of Pteris, 

 Hypolepis, Polypodium punctatum, runners of Dichsonia and of 

 Lomaria procera. 



If the creeping stem is extensively used for storage of starch 

 and water, then extreme polystely will be found. If the stem 

 is upright and the leaves crowded, a tubular stele, with leaf- 

 gaps, will result, as in the tree-ferns, and in a less developed 

 form in large forms of Polypodium pennigerum and Aspidium 

 aculeitum. 



The transition from the solid strand to the tubular form in 

 any particular fern now is not important from an historical 

 point of view. Perhaps the idea that in the ferns function in- 

 sures differentiation, and unless there is functioning to be done 

 no differentiation follows, suggests how th rt parenchyma appeared 

 in bulky stems in the first place ; and the same tendency results 

 in extreme polystely in some ferns now. 



But as far as the relationship between Dichsonia and Cyathea 

 is concerned, though no single similarity will prove anything, 

 yet the similarity of means employed in the young plants in 

 overcoming the environm ;nt at a great many points does point 

 to a similar inherited constitution. 



EXPLANATION' OF PLATES I-V. 



Plate I. 



Fig. 1. Transverse section, first leaf Dichsonia squarrosa. x 125. 



Fig. 2. Transverse section, petiole fi/st leaf Cyathea dealbata. x 250. 



end., endodermis ; ph., phloem ; p.c, dense perioyole. 

 Fig. 3. Transverse section, stele of same plant (as in fig. 2); starch »5. 



yet ab:iont. x 250. 

 Fig. 4. Transverse section, third petiole of Dicksonia ; collateral stele. 



x 175. 

 Fij. 5. Transverse section, potiole Dicksonia. In next leaf meristele 



breaks into three, x 125. 

 Fig. 6. Transverse soction, single bundle of mature petiole Dicksonia. 



x 80. pph., p.'otophloem ; s.t.p., sieve-tubo parenohyma ; &p., 



cavLy p irenchyma. 

 Fig. 7. Part of potiole bundle, showing relation between s.t. and paren- 



chymv x 175. x.p., parenohymi cells, rich in starch, lining 



the xylem cells. 

 Fig. 8. Another pirt of sam% showing cavity pirenohy ma. x 250. 



