56 Eric Drabble . 
THE TRANSITION FROM STEM TO ROOT IN 
t . * 
SOME PALM SEEDLINGS. 
By Eric Drabble. 
[Text-Figs 4 — 10 .] 
S EVERAL anatomists have endeavoured to trace the changes 
in arrangement of tissues accompanying transition from root 
to stem in the seedlings of palms. The difficulty encountered lies 
in the fact that lignification of the sclerenchyma generally precedes 
that of the xylem, and the highly sclerenchymatous nature of the 
axis not only obscures the xylem, but also prevents satisfactory 
manipulation of the plants by the ordinary microtome methods. 
Van Tieghem 1 examined Phoenix dactylifera L. and came 
to the conclusion that it agreed with his “ type I.” That is to say, 
the number of xylem and phloem bundles in the hypocotyl is 
half the number in the root, the transition taking place by the 
branching of each internal xylem group to right and left of the 
phloem group external to it, the protoxylem of each branch turning 
outwards during the process. The phloem groups remain in situ 
hitherto ; each now becomes separated from the next group by 
a pair of xylem branches with external protoxylem, which fuse to 
form a single group. 
Miss Sargant 3 in the course of her extensive work on 
seedlings also examined Phoenix dactylifera and Thrinax excelsa 
and found evidence confirmatory of Van Tieghem’s conclusions. 
Certain palm seedlings recently examined do not entirely 
agree with Van Tieghem’s description of Phoenix. 
The difficulty of satisfactorily tracing the whole course of 
events is considerable, but the points referred to below have not 
been recorded without carefully examining a long series of seedlings 
of both Phoenix dactylifera and Livistona mauritana. My thanks 
are due to Professor J. B. Farmer, F.R.S., and to Dr. Chandler, for 
fully examining my sections and for giving help on doubtful points, 
Phoenix dactylifera L. 
Differentiation and lignification of the xylem elements set in 
late. In a seedling so young that the plumule is completely 
enclosed within the cotyledonary sheath, the tissues are as yet in 
the procambial condition, and it is quite impossible to trace with 
any degree of certainty the details of transition. It is necessary, 
1 Van Tieghem. Traite de Botanique. 
2 Sargant, Miss E. Ann. Bot. Vol. XVII., 1903. 
