21 
al movements me b i similarly recorded on a horizontal sheet 
of p M— above the pla 
n this manner the — of a very great number of leaves have 
ie followod. The result of examination of a great number of such 
readings is to Bonga — picis ed the rachis begins to move upwards 
between 10 a at this upward movement is continued 
for about Mire peri: i. dl between 10 p.m. and midnight, and that 
then the rachis moves slowly down, reaching its lowest reading between 
10 and 12 next morning. In an entirely normal case, in which the con- 
ditions of illumination and temperature are fairly constant from day to 
day, the eurve of one day agrees with that of the preceding or following 
days, the leaf being m i rro at the same inclination at the same 
time on successive days. A single - M At about the horizontal 
in a single day will at one time (morning) be in a position segs 
(according to Mr. Nowack) relatively high i rometrie pressur 
later on in the same day in a position indicating relatively low raped ae 
ressu 
E: Thou; rh all the leaves show such a diurnal movement of the rachis, 
all have by no means an average horizovtal position ; some permanently 
those pointing downwards, on the other hand, will be nearer the horizon 
when at their maximum height (i.e., at night), nearer M" vertical in the 
morning. All the leaves on any plant move in the same din and 
each their greatest heights or depressions at the ane time, 
mean position of a leaf seems to he that position in which it will receive 
the most adequate illumination. This is strikingly shown when a plant 
is submitted to onesided vg antec as in an or inary room. The 
the upper surfaces of its leaves as far as mob at  right-angles to the 
i ight. After ini fo 
some time (a few weeks) this steep position becomes more or less fixed, so 
that if the plant be turned completely round through 180°, the position 
is not ei ipd e In the case of a leaf bending from a mean 
horizontal to a mean downward inclination y 60^, in re y 
onesided lum ination, the change of position is gradually achieved 
by successive sinking "day by day, a and failure to rise to the original 
elevation, Hence a leaf at first oscillating about a horizontal plane will 
after a time, step by step, be found oscillating about a steeply inclined 
lane. 
oes leaves, again, to accommodate themselves to light requirements 
will become elevated in a similar ma 
one, the extent of these daily movements is sli 
alier morning the downward movem ian is much rea than on a l arre 
loomy morning. e more intense light acts x 
s d the difference between the lowest da] -position and — t night E 
y the 
ber of plants under o tion at the 
ape s of obe: 27, 28, and 29, were dull and rather ees er 
those of the 30th and 31st € Vani Pn denies , dom 
dull in the morning though brightening up The 
ant curves etat the same period show that on the 27th, 280, ed 
