. Gray's school and field book of botany. Consisting of "Lessons in botany," and "Field, forest, and garden botany," bound in one volume. Botany; Botany. cerned under low powers of the microscope (Pig. 487), are the boundaries of the epidermal cells. 443. Breathing-pores, or Stomates, Stomata (singular, a Stoma, — literally, a mouth) are openings through the epidermis into the air-chambers or intercellular passages, always between and guarded by a pair of thin- walled guardian cells. Although most abundant in leaves, especially on their lower face (that which is screened fr
. Gray's school and field book of botany. Consisting of "Lessons in botany," and "Field, forest, and garden botany," bound in one volume. Botany; Botany. cerned under low powers of the microscope (Pig. 487), are the boundaries of the epidermal cells. 443. Breathing-pores, or Stomates, Stomata (singular, a Stoma, — literally, a mouth) are openings through the epidermis into the air-chambers or intercellular passages, always between and guarded by a pair of thin- walled guardian cells. Although most abundant in leaves, especially on their lower face (that which is screened from direct sunlight), they are found on most other green parts. They establish a direct communication between the external air and that in the loose interior of the leaf. Their guardian cells or lips, which are soft and delicate, like those of the green pulp within, by their greater or less turgidity open or close the orifice as the moisture or dryness varies. 444. In the White Lily the stomata are so remarkably large that they may be seen by a simple microscope of moderate power, and may be dis- cerned even by a good hand lens. There are about 60,000 of them to the square inch of the epidermis of the lower face of this Lily-leaf, and only about 3000 to the same space on the upper face. It is computed that an average leaf of an Apple-tree has on its lower face about 100,000 of these mouths. §5. PLANT FOOD AND ASSIMILATION. 445. Only plants are capable of originating organizable matter, or the materials which compose the structure of vegetables and animals. The es- sential and peculiar work of plants is to take up portions of earth and air (water belonging to both) upon which animals cannot live at all, and to convert them into something organizable; that is, into something that, under life, may be built up into vegetable and animal structures. All the food of animals is produced by plants. Animals live upon vegetables, Fig. 484. Small portion of epidermis of the lower face of
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