The 'dewdrops' on Lady's mantle aren't real dewdrops (at least most of them aren't). They are the result of a proces called 'guttation' (formation of droplets, guttae in Latin). When the water-saturation of the atmosphere is high (near 100 %), the plant isn't capable anymore to loose water by evaporation. It turns then to the proces of droplet-formation through open 'hydatodes' (water-mouths) at the edges of the leaves.
This proces takes place in most plants, but normally the drops fall on the ground. The special form of the lady's mantle leaves prevent them from falling, and they gather on the surface of the leaves.
On this picture you can see how the drops are formed on the leave's edge.
Alchemilla mollis, Lady's Mantle, is an herbaceous perennial plant native to southern Europe and grown throughout the world as an ornamental garden plant. It grows 30-45cm tall, with leaves that are palmately veined, with a scalloped and serrated margin. The chartreuse flowers are held in dense clusters above the foliage.
