Phylloglossum Drummondii , Kunze . 329 
about one plant in 2,000 may possess a forked strobilus, the two arms being 
equally developed. 1 
If, however, we hold that the tuber is morphologically a branch, 
branching in Phylloglossum can no longer be regarded as a rare occurrence, 
since it happens at least once in the yearly growth of every fertile plant. 
Moreover, the New Zealand form not infrequently produces more than one 
new tuber during the season, and in such cases two acts of branching must 
have occurred. 2 
When two new tubers are formed they may arise on opposite sides of 
the plant, with the old tubers between them (Fig. 2, b), or near together on 
the same side (Fig. 2, c). In this case the habit of the plant suggests that 
the two tubers are the result of a dichotomy, and this is supported by its 
stelar structure. A medullated stele is found in the peduncle, and is later 
interrupted by a gap, below which, on the same side of the plant, a curved 
band of xylem passes out into the cortex. So far there is close agreement 
with the stele of a fertile plant with one new tuber: the difference lies in the 
behaviour of the branch stele. Whereas it normally passes, with some 
modification in form, down the shaft of a single tuber, in the plant now 
under discussion it gives rise to two smaller strands, and thus supplies two 
tubers. The daughter steles are slender strands, showing no characteristic 
gaps, since the division takes place when the original stele is an irregular 
curved band of xylem. The duplication of tubers in this way is consistent 
with the conception of the tuber as a specialized part of the axis, and 
affords an example of double branching in Phylloglossum. 
Double branching also occurs in the axis of plants bearing a new tuber 
on two opposite sides. The anatomy of one of the three plants showing 
this feature has been fully described (p. 318), and, since the others agree 
with it in general structure, it is not necessary to do more than refer to the 
plan of the stele. 3 
A large stele is formed at the base of the plant by the entering root- 
strands. This divides, and the smaller product of the division supplies one 
of the new tubers. The larger of the two steles divides again, a small 
strand passing out to the second new tuber, while a large medullated stele 
passes up the peduncle of the cone. The distance between the two points 
of branching is so short that the tubers may appear to arise at the same 
level. That this is not the case is shown by the stelar anatomy (Figs. 3 
and 4, a). 
In these plants the new tubers have been formed by two successive 
1 Thomas : loc. cit. 
2 Thomas states that, while plants with one tuber are still in the majority, two tubers are 
frequently formed. 
3 In one case the axis apparently branches twice, but the stele of one new tuber is unconnected 
with the vascular tissue of any other part of the plant. This can only be regarded as an anomaly 
resulting from the reduction which the plant has suffered in the course of adaptation to its environment. 
