LI-COR occasionally receives inquiries from users of the LI-6400/6400XT Portable Photosynthesis Systems who want to measure gas exchange on only one side of their leaf, due to differences in leaf morphology (e.g. different stomatal ratios on either side of the leaf). This can be done fairly easily with the LI-6400 sensor head, by simply masking off the air supply holes at the bottom rear of the lower leaf chamber, as shown in the photo below. Use a short piece of clear cellophane tape to seal off the three holes shown. In this configuration, only the bottom surface of the leaf will be measured.