The leaves have two distinct parts: the top and bottom. Although we call them that, they are really what make up the foliage of plants. There can be no back without beam, nor vice versa When one part is damaged, in the other it will be possible to see some symptoms as well.
For this reason, I like to say that the leaves are the mirror of the plants, since when they have problems it is on the upper side and on the underside where the first symptoms appear, almost always. However, what are their characteristics?
What is the beam?
The beam is the upper face of the blade of a leaf, the part that is most exposed to light. Therefore, it has a thicker cuticle, since in this way it can protect itself better. In addition, it has fewer trichomes, which are like hairs found in the epidermis and which perform multiple functions, such as absorbing water or regulating the temperature of the plant.
In general, the beam is darker in color than the underside, precisely because its exposure to light is more direct than that of the latter.
What is the underside of the sheet?
The underside is the underside of the leaf. It has a somewhat thinner cuticle, and a greater number of both stomata and trichomes. In addition, its color is usually darker. Sometimes these trichomes, or hairs, are whitish in color, as is the case with those of the the white.
Some plants have the underside of a color very different from green. For example, many begonias have it purple in color. Why? This is an adaptation measure. Begonias, many of them, live in forests and tropical jungles, under the shade of trees and palm trees. In these low light conditions, the few solar rays that filter through and reach the underside are used to the maximum.
Where are there more stomata: on the upper side or on the underside?
Stomata are the pores of the leaves, and are found mainly on the underside. Gas exchange takes place through them: during photosynthesisThey absorb oxygen (O2) and expel carbon dioxide (CO2); during perspiration they expel water vapor; and with breathing they absorb O2 and expel CO2.
To avoid excessive water loss, during the summer they are kept closed during the hottest leaves of the day. In this way, they can perform their functions later, when conditions are better.
As you can see, the top and the underside are two very important parts for plants.