216 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
may, in a few cases, possibly be of considerable, or even of primary, im- 
portance. 
Correlation of Growth under the Influence of Injuries.* — From 
experiments, made chiefly on seedlings and on Phycomyces , Mr. C. 0. 
Townsend draws the following general conclusions : — A single irritation 
produced by cutting or splitting the shoots or roots, or removing the 
leaf-tips of seedlings, tends to produce a change in the rate of growth of 
the injured and of the uninjured parts. If the injury is slight, signs of an 
acceleration in the rate of growth will be apparent in from 6 to 24 hours, 
and will continue for from one to several days. If the injury be severe, 
the acceleration will be preceded by a period of retardation of longer 
or shorter duration, depending upon the severity of the injury and upon 
the condition of the plant injured. The growth of the stem of older 
plants is accelerated by the removal of a number of the roots or leaves, 
but is not affected by a slight injury to the root. The roots of older 
plants, as well as of seedlings, are more independent than are the stems 
and shoots. The change in the rate of growth of higher plants under the 
influence of a single irritation begins gradually, reaching its maximum 
in from 12 to 96 hours, and gradually diminishes until the normal rate 
is resumed. The total variation in the growth of higher plants due to 
the influence of a single irritation, is from zero to 70 per cent, of the 
normal growth for the same period. The growth of sporangiopliores 
of Phycomyces is suddenly and strongly retarded by cutting either the 
mycele or another sporangiophore on the same plant. The growth does 
not entirely cease, and gradually recovers its normal rate in from 30 to 
60 minutes. The influence of an irritation due to cutting or other injury 
is capable of acting through a distance of several hundred millimetres. 
Hygroscopic Function of Stomates. f — By the method described on 
p. 134, Prof. F. Darwin has arrived at the following conclusions with 
regard to the action of stomates. When leaves have stomates on the 
under surface only (hypo-stomatal), there is a low degree of transpiration 
for that surface. On the under surface of floating leaves ( Nymphsea ) 
there is active transpiration when exposed to the air. In a terrestrial 
leaf with stomates on both surfaces, those on the upper surface are more 
sensitive to external conditions, and are frequently shut when those on 
the lower surface are open. The typical stomate closes either wholly 
or partially in darkness, the process being a gradual one ; the nocturnal 
closure is a periodic phenomenon. When a leaf is removed from the 
plant, the stomates close, owing to the diminished turgescence of the 
guard-cells. The opening of stomates must be due to the loss of turgor 
in the other elements of the leaf, especially of the ordinary epidermal 
cells, the final closure being due to the withering of the guard-cells. 
Influence of Electric Currents on the Lower Organisms.:]: — Ac- 
cording to Dr. K. Heller, a continuous electric current exercises a pre- 
judicial effect on filaments of Cladophorci and Spirogyra , ultimately 
killing them. On the diatoms the effect was but slight, as was also 
the case with Oscillatoria. Mucor stolonifer displayed strong powers of 
* Ann. of Bot , xi. (1897) pp. 509-32. 
f Proc. Cambridge Phil. Soc., ix. (1897) pp. 303-8. 
t Oesterr. Bot. Zeitschr., xlvii. (1897) pp. 326-31, 358-61 (1 fig.). 
