Considered in Relation to its Function. 4 1 1 
of the chloroplasts, was medianly situated (Fig. 2). The crack, of course, 
is only visible in certain planes, and as some of the chloroplasts rolled 
over, it was possible to see it appear and disappear. 
A similar crack could be obtained by irrigation with dilute salt solution. 
But these cracks never appeared in con- 
centrated solutions of either salt or sugar. 
When the concentrated salt or sugar 
solution in which the granules are lying is 
gradually diluted, at a certain degree of 
dilution the split rapidly appears in a 
number of the granules. In most cases it 
appears simultaneously across the whole 
width of the granule, but in one or two 
cases it was seen first at one side, afterwards 
extending rapidly across the chloroplast. 
When the split has once appeared, it is 
impossible to make it disappear by increas- 
ing the concentration of the surrounding 
solution, so that it seems to represent some definite structural change in 
the granule. 
The split is never followed by the complete separation of the two 
halves of the chloroplast, though in some cases (see Fig. 2) it is impossible 
to see any connexion still holding the two parts together. 
Usually the crack is very regular in its outline, especially in the case 
of the symmetrical granules of Chlorophytum. In the less regular granules of 
Selaginetla , the crack was more variable in its nature, and in some cases 
the granule appeared to have split into three parts. 
Some of the split chloroplasts of Selaginetla were frozen and cut. 
In these it was possible to discern places where the green layer was dis- 
continuous in the usually uninterrupted rings. This indicated, presumably, 
the region in which the crack had occurred. All these observations were 
made on the chloroplasts of Chlorophytum and Selaginetla , but the split 
can readily be shown in the chloroplasts of many plants, when similarly 
treated ; for example, we have seen it in the Geranium , Coleus , Elodea , Iris i 
and Amaryllis. 
Effect of Light and Carbon Dioxide on the Splitting. 
It was thought that even after expression in sap, the chloroplasts might 
still be able to form sugar. If this sugar were still retained within the 
chloroplast there should be a difference of osmotic pressure, comparable 
to that previously obtained by diluting the surrounding medium, and under 
the circumstances, a crack might be expected to appear. Leaves of 
vS. Martensii and Chlorophytum were placed in water in a dark cupboard 
Os 
Fig. 2. 
