1 1 6 Brebner . — On the Prothallus and Embryo of 
only one thin-walled element. Passing upwards, the thin- 
walled tissue in question increases in amount till it becomes 
recognizable as part of the phloem of the primary stem. With 
regard to the xylem, the details of the junction of the stele 
of the root with that of the stem could not be made out with 
anything like certainty ; this was also the case with regard to 
the transition from the xylem of the stem to that of the coty- 
ledonary trace. All that can be safely said is that in both 
cases the elements in the transitional region seem to be 
exclusively scalariform tracheids 1 . The stele of the primary 
stem has a well-marked endodermis (Fig. 20, en.), and in this 
Danaea agrees with Angiopteris 2 , but differs in not having 
a central mass of parenchymatous tissue. Fig. 20 shows the 
stele just about to divide to form the traces of the cotyledon 
and of the second leaf. In some cases, as already mentioned, 
the xylem of the cotyledon consists of only two elements, 
arranged side by side in the tangential plane. In such a case 
it is obviously impossible to speak of a protoxylem as dis- 
tinguished from a later formed xylem. In cotyledons with 
more vigorous bundles, protoxylem is readily enough recog- 
nizable on the inner (axial) side ; it is not, however, composed 
of spiral elements, but of delicate tracheids of narrow calibre 
with wide scalariform pits. The arrangement of the steles 
in the stem of young and older plants need not be discussed 
here 3 , but the mode of succession of the first three leaves is 
exactly the same as in Angiopteris, as described by Prof. 
Farmer 4 , and thus the first part of the spiral is laid down; 
the anatomy, however, becomes subsequently much compli- 
cated by anastomoses of the steles. The adventitious roots 
seem to arise much later than in Angiopteris , in which the 
second leaf already has its accompanying adventitious root 
1 The series of microtome-sections obtained through the parts in question were 
not very successful, and the young plants were not at the best stage for the purpose. 
2 Leclere du Sablon, Recherches stir la tige des fougHres. Ann. des Sciences 
naturelles, 1890, T. ii. 
3 This question will be more fully treated in a paper on the comparative 
anatomy of the Marattiaceae, which is in process of preparation. 
4 Loc. cit., p. 270. 
