Where the colour changed

Hold your drawing next to the tested leaf. The blue-black appears exactly where the green used to be, and nowhere else.

Figure to be added

Figure 2.9 — the same variegated leaf twice. On the left, before the starch test: a leaf with green regions and irregular white patches, both labelled. On the right, after the starch test: the patches that were white are still pale and labelled as showing no colour change, and the regions that were green are now dark purple or blue.

The observation

In the white or variegated places there is no colour change, while in the remaining parts a blue colour shading towards dark purple is observed.

Reading the result

Starch has not been produced in the white or variegated places of the leaf. Since chlorophyll is not contained there, photosynthesis has not taken place.

The conclusion

It can be concluded that chlorophyll is necessary for photosynthesis.

This is the definition proving itself

The chapter began by defining photosynthesis as something that happens inside cells containing chlorophyll — not in plants, in cells. Here is a single leaf, on a single plant, in a single patch of sunlight, in which one group of cells photosynthesised and the group of cells beside it did not. Nothing distinguishes them but the pigment.