412 Priestly and Irvings — The Structure of the Chloroplast 
for three days ; the granules were then extracted under pressure, and upon 
examination they showed no split. Drops of sap containing the chloro- 
plasts were then mounted on microscope slides in the ordinary way ; and 
all the slides were placed in a moist atmosphere in the greenhouse, some 
being kept in a sunny position, others in the dark. 
It was found that in the slides which had been placed in the sunlight, 
about 80 per cent, of the chloroplasts had split, whereas a crack had appeared 
in 5 per cent., at the most, of those kept in the dark. 
Fresh slides, prepared in the same way, were then mounted under two 
bell-jars both in the light, a beaker containing caustic potash being placed 
in one of the jars, and water in the other. 
After having been left for a week, it was found that none of the 
granules in the atmosphere free from carbon dioxide had split, and would 
not now do so, even when placed in distilled water. The other set showed 
the crack in the usual manner. 
These experiments seem to indicate that when the granules are isolated 
in this manner, they are still alive, and capable of synthesizing sugar from 
carbon dioxide, and water, in the presence of light. The sugar thus formed 
collects within the granule, while the outside medium remains at its former 
osmotic strength, and consequently, a split occurs just as when the sap 
is diluted. 
The Effect of Chloroform . 
Leaves of Selaginella and Chlorophytum were killed by treatment with 
chloroform vapour for two hours. The juice was then expressed as before, 
and the chloroplasts mounted in distilled water. 
In this case it was quite impossible to see any split in the granules. By 
placing them in a dilute solution of eosin, it was seen that the outer 
membrane of the plastid had been rendered completely permeable by 
the action of the poison, the eosin passing into the granule, and colouring 
it, but not concentrating within it, as it does when the chloroplast is 
living. 
The Nature of the Split. 
This split then can be brought about in the chloroplast either by 
decreasing the concentration of the surrounding sap, or by increasing the 
concentration of the sugar solution within the granules. 
It seems, therefore, to be the result of an internal swelling caused 
by water passing into the chloroplast, and of the consequent separation 
of the outer peripheral ring into two halves, the inner colourless stroma 
not dividing, but holding the two together. 
The passage of water inwards may be due to a difference of osmotic 
pressure on either side of the peripheral layer, which functions as a semi- 
