52 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Periodicity in the Growth in Thickness of Trees.* * * § — Herr J. Wieler 
criticises the statements of previous writers on this subject, and gives the 
result of observations of his own. In even closely contiguous spots the 
growth in thickness of trunks is often very far from uniform. There are 
in general, both with Conifers and Dicotyledons, two periods of greatest 
activity, about the beginning of June and the middle of July. This 
later period of activity is subject to very great variations. The period 
of greatest activity in the development and unfolding of the buds does 
not necessarily agree with that of the cambium. 
Periodical Growth in Hevea brasiliensis.f — Herr J. Iluber calls 
attention to the intermittent growth in this rubber-producing tree, which 
may be divided into three phases: — (1) A rapid elongation of the axis, 
both between the upper bud-scales and between the succeeding young 
leaves; (2) The development of the leaves in the succeeding phase, 
during which they attain their full size, but hang limp ; (3) The full 
development of the tissue of the leaf, when the leaves gradually assume 
a nearly horizontal position, with their characteristic consistence. Each 
phase may extend over about ten days, with intermediate pauses of about 
the same length. 
Dormant Life in Bulbs and Tubers.J— M. Leclerc du Sablon points 
out that in bulbs and tubers the resting period is not the winter, but 
the summer, vegetation commencing again in the autumn. They have, 
therefore, to protect themselves rather against drought than against 
cold. The reserve carbohydrates are chiefly starch, inulin, dextrose, and 
saccharose ; glucose is rarely present, except in Allium and Aspliodelus. 
During the period of repose, chemical changes are going on in the reserve 
without any external change in form; digestion has commenced; and 
the bulb or tuber is brought into a state fit for germination ; diastases, 
which were almost entirely wanting at the commencement of that period, 
being gradually formed. 
Growth of Arum maculatum.§ — Mrs. R. Scott and Miss E. Sargant 
have followed out the growth of this plant from the seed, which is 
exceedingly slow, the first leaf not appearing above the ground till the 
third year, nor a flowering shoot till the seventh. During the first two 
years there is no formation of chlorophyll in any part of the plant ; 
the contractile roots have a most powerful effect in dragging it below 
the surface. The internal morphology and histology of the young 
seedling are described in detail. 
Change of a Perennial into an Annual Plant. || — From observations 
made on the scarlet-runner, Phaseolus multiflorus, Dr. R. v. Wettstein 
has come to the conclusion that it is originally, in its native state, a 
perennial plant ; and that it has been unable to hibernate with us, owing 
to our climatic conditions, and has hence become annual under cultiva- 
tion. By altering the conditions, he was able to maintain life in the 
same individual for four years, but with diminished vigour. 
* Tharander Forst. Jahrb., xlviii. (1898) 100 pp. See Bot. Ztg., Ivi. (1898) 2 te 
Abth., p. 260. t Bot. Centralbl., lxvi. (1898) pp. 259-64. 
t Comptes Rendns, cxxvii. (1898) pp. 671-3. 
§ Ann. of Bot., xii. (1898) pp. 399-414 (1 pi.). 
|| Oesterr. Bot. Zeitschr., 1897, No. 12, and 1898, No. 1 (13 pp., 3 figs.). 
