415 
the Effect of Formaldehyde on Living Plants . 
six centimetres across, filled with dry sand. The sand was then moistened 
with distilled water, and the cultures set on glass tripods in a large bath of 
water. Where carbon dioxide was to be excluded, this watei contained 
io per cent, of stick potash, and where the air contained caibon dioxide 
a little calcium chloride was added to the water to prevent algal growths. 
A weighed waterer containing nutrient solution was set above each culture. 
Then a glass bell-jar, supported on the edges of a large porcelain ‘ develop- 
ing dish was inverted over each culture (or pair of cultures) so that its 
rim was covered to a depth of about three centimetres by the water or 
potash solution in the bath. The only connexion with the outside was now 
through the air inlet- and exit-tubes, which dipped, through the solution in 
the bath, under the rim of the bell-jar. 
The Watering of the Seeds. — The Automatic Waterer. 
The solution to this problem gave the key to the whole investigation. 
A watering apparatus was required which 
would give small and regular quantities 
of water over a considerable period of 
time, and, if possible, introduce no organic 
substance, such as rubber tubing, into the 
gas globe. After experimenting for about 
eighteen months with various forms of 
siphon -tube, connected with a reservoir, 
outside the gas globe, through which 
water could be introduced by a tap worked 
by hand, it was found that all such methods 
were highly unsatisfactory. 
An automatic waterer was then de- 
vised, of which Text-fig. 2 is a diagram- 
matic sketch. It is composed of a glass 
reservoir drawn out into a narrow outlet- 
tube below. Two glass tubes were sealed 
into the top of the reservoir. One of 
these was drawn out into a fine end, which 
could be opened for filling the apparatus 
and then sealed again with a blowpipe, 
a long piece of capillary tubing, conveniently bent to form a stand for 
the apparatus. The principle upon which its action depends is very simple. 
The apparatus is filled by putting the outlet-tube under water and applying 
suction at the open end of the filling-tube. The end of the filling-tube is 
then sealed over. Now no water can escape from the apparatus until an 
equivalent volume of air has entered the space above it. There are now only 
two possible entries for air : one is through the water, of which more later ; 
Text-fig. 2. 
The other tube was sealed into 
