100x Magnification

Notice the dense, compact cell layers forming the epidermis of this leaf. These help form a very durable epidermal surface with a thick cuticle. Some of these cells will be identifiable at higher magnification as sclerenchyma fibers. Due to the presence of these tissues, conifer leaves are classified as sclerophylls.

Pine leaves possess an endodermal layer around the vascular tissues. This is another adaptation to prevent water loss. This layer can be seen surrounding the xylem and phloem in the top part of this image.

200x Magnification

In a 200x view, details of this sclerophyll are emerging. Look for the sclerenchyma fibers in the epidermis. Sclerenchyma cells, with their lignified secondary cell walls, create a strong, protective epidermis that makes the conifer leaf a very durable structure. Remember, with very few exceptions, conifers hold their leaves for several years while deciduous species lose theirs yearly.

Sunken stomata of the epidermis are now visible in this view. These represent yet another adaptation to limit water loss.

400x Magnification

Notice the two specialized cells on either side of the stomates. These are the guard cells.

The stomata of most leaves open during photosynthetic activity to allow efficient gas exchange. However, this brings a penalty in the increased transpirational water loss that can occur due to convective air currents. Sunken stomata like these help minimize convective water loss under hot, windy conditions.

1000x Magnification

At 1000x magnification the dense cuticle of this epidermis is more visible. Guard cells on either side of the stoma stand out as highly specialized cells. Note the open pore where gases are exchanged across the leaf surface.

Water loss within leaf tissues causes shifts in osmotic conditions within guard cells. The resulting osmotic conditions create physical forces that deform the guard cells, causing them to close stomatal pores. This effectively decreases further water loss from the leaves.