556 SECTIONAL TRANSACTIONS.—K,. 
explanation, though not going so far, has been put forward by Du Buy for 
the phototropic curvature of oat seedlings. 
Dijkman, studying the geotropic curvature of seedlings of Lupinus, has 
shown that here also the explanation of Dolk holds good. When these 
seedlings are placed in a horizontal position the distribution of the auxin 
is altered, the lower half getting more than the upper one ; consequently it 
must grow faster, and a negative geotropic curvature results. ‘The amount 
of the curvature may be calculated from the distribution of the growth 
substance. 
Bottelier has made a study of protoplasmic streaming in the coleoptile 
of Avena. The influence of temperature is small in young plants, but in 
older ones he obtained a ratio for the velocity of streaming at 16:5° C. to that 
at 24° C. of 10 to 21-3, which is almost identical with the ratio found by Van 
der Wey for the velocity of the transport of auxin. Light, especially of short 
wave-length, has a very pronounced influence on the velocity of protoplasmic 
streaming ; it is very remarkable that this influence is almost the same as 
in the light-growth reaction according to the data obtained by Van Dillewijn 
several years ago. 
The amount of protoplasmic streaming was not always the same, but it 
became evident that it changed with the sensitivity of oat seedlings to the 
growth substance. This amount is small when the sensitivity is low, and 
greater with a higher sensitivity. 
An investigation into the factors which influence this sensitivity in a room 
kept at constant temperature and constant humidity is in progress under 
the auspices of Kégl, and is being carried out by Haagen Smit and J.J. Went. 
There is sometimes a certain periodicity in this sensitivity, so that at a 
certain time of the day it is high, at another time low. ‘They could get rid 
of this periodicity by the use of metal boxes in the constant temperature 
room. Whilst it was not necessary to make use of leaden boxes, they had 
to be made of a good conductor of electricity. Hence it was clear that 
cosmic rays had no direct influence on the phenomenon, but possibly the 
electrical conductivity of the air played some part in it. The investigators 
could alter the sensitivity of the seedlings by passing a feeble electric current 
through them. When the tip is negative with respect to the base the sen- 
sitivity is lowered ; in the opposite case it can be carried up to an amount 
never yet found under natural conditions. ‘The currents necessary for 
obtaining the same deviations of the sensitivity as under natural conditions 
were of the order of 10-§ ampere. Oat seedlings are remarkably good 
objects for such experiments, since the effect can be quantitatively measured 
in them much better than in other cases. 
Miss E. N. SparsHott.—Tuberisation, with special reference to the 
development of Testudinaria elephantipes (10.40). 
The adult tuber of Testudinaria elephantipes is semi-globular with a 
flattened base from which roots arise centrifugally. Except at the apex 
the surface is covered with cork, thin over the base, but thick and deeply 
fissured elsewhere, owing to internal growth. Each season one or more 
new climbing vegetative shoots develop in the axil of one of the scale leaves 
surrounding the apex of the tuber. 
The embryo shows no tuberisation. The plumule remains very short 
and bears one relatively large leaf. Assimilates accumulate in the hypo- 
cotyl, which rapidly undergoes tuberisation. Early thickening results from 
division and hypertrophy of existing cells. 'Tuberisation is continued by 
secondary growth mainly from a pericyclic ‘ growth zone,’ but also from 
