Leaves have three main parts:  The petiole, a stalk-like structure that connects the blade of the leaf to the stem of the plant. Some leaves don’t have petioles,  and are known as sessile leaves. The blade or lamina, usually the largest part of the leaf.  The edge of the leaf or the leaf margin may be described as entire, toothed, or lobed. The oak leaf, for example, is clearly lobed. The blade has many veins, forming a network, carrying water and nutrients, The base, the base is the region of the blade that attaches to the petiole. A leaf is said to be simple if its blade / lamina is undivided, if the ‘teeth’ or lobes do not reach down to the main vein of the leaf.  A compound leaf has several leaflets, which join up with a single leaf stalk or petiole. When identifying tree leaves, it is always important to look for the petiole,   as a single leaflet of a compound leaf can look like a simple leaf.  More details of leaf and tree structure can be found on this link on our website. Now for a challenge.  Can you or your children find a leaf (and name the tree it came from), that Has a serrated / toothed edge Has a lobed margin Has a smooth edge / margin Is a compound, palmate leaf Is a compound, pinnate leaf Is hairy Is not green, but red or a mixture of colours Is more or less circular Is fleshy / succulent Has spines on its edges Is needle shaped Has a thick (waxy?) cuticle or is very shiny Has net venation  is marcescent (might keep you hanging around) Go forage!

Climbing plants like sweet peas can ‘feel’ their way around a support, a twig or fencing. Charles Darwin, who had an interest in climbing plants, described Clematis as a leaf climber.  Clematis has compound leaves with three to five leaflets,  It uses the stalks of the leaves or the leaflets to climb. Darwin noted that contact with another structure was enough for the leaf stalk / petiole to start bending around it.  This ability to respond to touch is termed thigmotropism.  It is a growth response.   The growth rate on the side of the stem that touches the 'support' is slower than on the side opposite the point of touch.  As a result the stem begins to curl around the support.  The same response is seen in plants that climb using tendrils, such as White Bryony.  Its tendrils are thin, wiry structures along the stem that ‘reach out’ into the space around a plant until they come into contact with something they can ‘grab’.  Once contact is made, the tendril curls, forming a coil. This sense of ‘touch’ has recently been investigated using Thale or Mouse Ear Cress.  It has been shown that the veins of the leaves respond to touch.  The investigators used small glass beads to apply a small but distinct pressure, and recorded a series of rapid electrical signals (not dissimilar to those seen in nerves).  Even when the veins were removed from the surrounding leaf tissue, they still showed electrical activity so the response was not reliant on surrounding cells.  The electrical activity was also associated with proton pumps (moving hydrogen ions).  The sensitivity of the veins to touch may be associated with the plant’s defence mechanism.  Animals like aphids use their mouthparts (stylets) to penetrate the vascular tissue in the veins.  The jasmonate system is involved in wound response. Another plant, the Venus fly trap (Dionaea muscipula), also responds to touch. It catches prey (insects and spiders) by means of touch.   Dionaea catches its prey with a trap, formed from the terminal portion of each of the plant's leaves.  The trap is activated by tiny hairs on the inner surfaces of the trap. When a hair is touched by an insect or spider crawling along the leaves, the trap prepares to close but it only snaps shut  if the hairs are touched again, within approximately twenty seconds of the first stimulus.  

The maidenhair tree is otherwise known as Ginkgo biloba, or just Gingko is native to China, but is widely cultivated through the world.  The name Ginkgo may be derived from a misspelling of the Japanese Gin kyo or silver apricot - referring to the form of its fruit.   The biloba part of the name refers the two lobed form of the tree’s leaves. Ginkgo is a dioecious species, that is to say, there are separate male and female trees.   The female tree produces quite large seeds within a yellow brown soft fruit-like structure.  Though attractive in appearance, it has a a rancid smell.  The smell is due to butyric acid in the fleshy part of the fruit; and for this reason it is male trees that are usually cultivated.   The male trees produce small cone-like reproductive structures, not dis-similar to those seen on other gymnosperms. Read more...

Phytomyza ilicis is a (dipteran) fly that lays its eggs in holly leaves.  It is one of the few insects that is able to make use of holly leaves as a food source and somewhere to live (when a larva).  The female fly lays eggs in the holly leaf (near the main veins or midrib – on the underside) using a thin tube or ovipositor.  The eggs are usually laid in early Spring when there are young and ‘soft’ leaves.  Older leaves have a thick and tough cuticle that is far more difficult to penetrate.  The larvae or maggots emerge from the eggs and tunnel their way along the midrib / veins emerging some time later into the lamina or blade of the leaf.  Here they feed on the photosynthetic tissues of the leaf – the palisade and mesophyll layers, creating a leaf mine (see featured image above).  The number of leaf mines per leaf is a maximum of three and often just 1 or two. Read more...