Development of Chlorophyll. 807 
cell measures 7-| inches by 4% inches by inches, and the lower part 
contains a stratum of broken pot on which the grains (100) are germinated. 
A cork at one side admits three tubes, and the cell can be closed above by 
a thin glass plate waxed down air-tight. The air current enters at B and 
leaves the chamber by A. During the early stages of growth the jar, not 
yet sealed at the top, is kept completely darkened. Every other day the 
stagnant water is drawn off by c and fresh water is added from above, 
C being now closed by a clamp. When the seedlings have reached the 
desired age, the lid is sealed on, and the jar brought out of the dark room 
and placed within one inch of a north window in the laboratory, with 
a white paper screen behind it. It had previously been ascertained that the 
diffuse light in this position is strong enough to enable green seedlings to 
assimilate practically the whole of their own respiratory C 0 2 . 
Fig. 2. 
In Exp. I the jar was set up in the window five days after sowing the 
seeds, when most of the plants showed the first colourless sheathing leaf-base 
one inch tall, and none of the functional leaves had yet burst through the 
tip of the sheath. The intention was to follow the development with the 
natural alternation of day and night, and see how soon the power of 
photosynthesis would be equal to assimilating the bulk of the respira¬ 
tory C 0 2 . 
Fig. 2 shows the magnitude of the carbon-dioxide output measured 
continuously for five days. The periods of natural darkness 7 p* 5 a * m * 
each day are shaded in the diagram. The stepped curve shows the 
respiration in grams per hour for the 100 seedlings, estimations being taken 
every three hours by the procedure mentioned on p. 809. The days were 
very dull throughout and the temperature in this spot was between 18 0 and 
20° C. by day, falling to 15° or id°C. by night. The readings began at 
10 p. m. on August 18. On August 19 there were still no leaves through the 
sheath, and by day respiration rose with the temperature, falling again 
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