The leaf

If we asked you to point out where the laminar appendix of a plant stem, would you know where to point? Probably not: and if instead, we asked you to indicate a leaf? We can take for granted that leaves are the green part of plants, but what else do we know about them? First, we should say that leaves have two faces, called the upper and lower pages by botanists. All leaves are formed by two elements: the lamina, which is the expanded and flattened part, and the leafstalk, the sort of central branch that keeps the leaf attached to the stem. The connection with the stem can be of different kinds: a sessile leaf is when you do not see the stem and the leaf is attached directly to it. Instead, when the leafstalk is inserted on the stem and circles it, you are looking at an amplexicaul leaf, and finally, when the lamina is wrapped directly around the stem and clings to it like a sheath, it is called a sheathing leaf. Leaves are the power station of the plant because they favor the exchange of gas with the atmosphere and prevent transpiration from causing an excessive loss of moisture. It is essential, in fact, that the amount of water absorbed by the roots not be inferior to that amount lost by transpiration: this botanical rule is known as water balance.