<human>:  With regards to the structure of a leaf, how many cells are there in a leaf?
<bot>: That depends on the leaf. Some leaves have more cells than others. The number of cells in a leaf is usually a multiple of the number of cells in a stem, which is called the branching order. The leaf is usually made up of a series of layers of cells, called the palisade layer, the spongy layer, and the vascular layer.