Stephenson. — Young Stages of Dicksonia and Cyathea. 9 



between two and five, the number partly depending on the 

 branches given off. 



When lignification of the cortex is taking place a few cells 

 — especially well marked in C. Cunninghamii — opposite the 

 oligogenetic rows remain thin-walled for some time, probably 

 as long as they are likely to produce lateral rootlets. The 

 endodermis stains deeply in acid fuchsin, but the oligogenetic 

 rows do not stain. 



The mature roots of C. medullaris are more robust and more 

 variable than the others. Triarch and even tetrarch bundles 

 are sometimes found (De Bary). This calls to mind the poly- 

 arch bundles in the Hymenophyllacece. 



The Vascular System op the Stem. 



The tracheids are scalariform in the foot of the embryo, 

 but become spiral in first leaf and root. 



Figs. 25-29 show the changes in the stele at this stage as 

 we ascend from the root (fig. 25) to the protostele above the 

 foot. The tracheids, at first extended in a line (fig. 26), become 

 clustered as the foot is reached (fig. 27) and turn into a hori- 

 zontal position. They turn into the vertical position again, and 

 now the phloem is clustered to one side in the collateral bundle 

 of the petiole. 



The tracheids of the second leaf fit directly on to those of 

 the first, and so a solid strand is found. But there is generally 

 a change from the protostele to the tubular form of stele before 

 the third leaf is given off. But the time is very variable, and 

 in Cyathea dealbata especially the protostele may persist for 

 five or six leaves. Sometimes the transition took place between 

 the foot and the insertion of the first leaf (figs. 85-88). Here 

 a few parenchymatous cells appear among the xylem elements 

 (fig. 86), and rapidly increase in number (fig. 87), and then 

 the segment is given off to the leaf. Figs. 79-81 show the third 

 leaf given off in C. dealbata from a protostele. Here a parenchyma 

 cell appears in preparation for the giving-off of the leaf, as in 

 Dicksonia. But generally the transition in Cyathea is more 

 irregular. Figs. 37-41 show the process in C. Cunninghamii. 

 The sections are of the internode between the first and second 

 leaves. The number of tracheids remains almost constant during 

 the change. ci..„. / -^ <-. _^ 



i:S ^ o or' 



' 2 3 a 



Diagram of Xylem, showing Transition. 

 (a.) Part directly below third leaf, (b.) Cauline part, (c.) Part below 

 second leaf, (d.) Tnird leaf given off here a little above, (e.) Second 

 leaf now given off here. 



