14 
NATURE NOTES 
Hydrotropism. — Another property characteristic of roots is a 
sensitiveness to water. An interesting experiment of Sachs’ 
illustrated this “ turning water-wards.” Take a square piece of 
coarse wire gauze, bend it so as to make a trough and fill it 
with wet moss, then place some well-soaked beans within the 
moss. The gauze must be suspended in a slanting position. 
When the beans have developed their radicles, as soon as they 
protrude below, the moist surface being closer to one side of the 
tip, since the gauze stands at a steep angle, the attraction for 
water overcomes that of gravity ; the result is that the tip bends 
back and re-enters the moss ; but now gravity reasserts itself, 
and the tip comes out again, to repeat the process, so that it may 
thread itself in and out of the gauze. 
Aphercotroptsm. — “Turning away from an obstruction” is a 
peculiarity discovered by Darwin. His experiment was as 
follows ; — After allowing a radicle to be well developed in peas, 
beans, &c., the seed is suspended in the air. A tiny piece of 
card is attached to one side of the tip by a little gum ; the tip will 
now move away from the vertical position, on the opposite side 
to the card. The tip may make one or more complete circles in 
a vertical plane ; and it has been known to pass through the 
first loop so as to tie itself into a knot. This explains how a 
radish was once dug up and found to be thus tied up. 
The Shoot ; Circumnutation. — This a.nd phototropism, or “ turn- 
ing light-wards,” induces the stem, whether it be the radicle, 
“ hypocotyl ” in mustard, or plumule “ epicotyl ” in the bean or 
oak, to rise up into the air. In the latter instance the plumule 
first grows in the form of an arch ; and if it be beneath the 
soil, by circumnutating it is enabled to free itself from the earth 
above it, and so gets out into the air. It then straightens itself 
and grows vertically upwards. This upward growth is due to 
the sensitiveness of the apex to light ; for if a box have the 
bottom removed and be provided with a gauze shelf below the 
lid, and if seeds be sown on earth on the shelf and the lid be 
now closed, the box being supported so that the interior can only 
be illuminated by reflection from a mirror below, then the 
shoots are found to grow downwards, i.e., towards the light and 
in the direction of and not in opposition to gravity. 
Respiration. — Seeds when germinating recjuire air, moisture 
and a fitting temperature. The air supplies oxygen gas, so 
that the living protoplasm may respire ; for respiration is as 
absolutely necessary for plants as for animals. The protoplasm 
absorbs oxygen, which then combines with carbon liberated by 
chemical decomposition of substances containing it. It is then 
given off as carbonic acid gas. To prove this, let a quantity 
of well-soaked peas or beans be put into a glass bottle having 
a wide mouth and well-fitting stopper. Let it be placed in the 
sun or warmed, as heat intensifies respiration in plants. After 
a time, so much carbonic acid will have been produced at the 
expense of the oxygen that, if a lighted taper be carefully and 
