Bright green patches of bog moss (Sphagnum) thrive in wet hollows on the fell tops. Step into one of these and you’ll suddenly find that you’ve got a boot full of water, because this moss acts like a living sponge. Each plant constantly grows from its apex and dies from its base and the accumulated weight of living plant crushes layers of dead moss underneath, which ultimately form peat. It’s the plant’s ability to retain water, even in dry summers, that makes Sphagnum bogs such important wildlife habitats for moisture-loving wildlife. You need to look at the minute leaves under the microscope to see how they do this. Magnify the leaves a little and you can see that each leaf is a network of cells. Increase the magnification a little more and two kinds of cells are revealed – green photosynthetic ones (the living part of the leaf) and empty, transparent dead ones. The photosynthetic cells form a living network, enmeshing the dead ones. Increase the magnification further and you can see the structure of each dead cell, it’s shape maintained by beams of thick cell wall material, with a hole in each cell wall. Once these dead cells fill with water capillarity holds it firmly in place. Squeeze the moss and water flows out like water from a sponge. Tread on one of those bright green patches and the water fills your boot..........and then it's wet socks for the rest of the walk.