Firstly, some questions. Now, no cheating and you really should write down the answers.
Question one. (An easy one to give you confidence) Does nectar contain dilute honey?
Question two. Are nectar and honey of the same composition, even if honey has less water?
Question three. Where is nectar made? (Precision needed here!)
Question four. How does it get out of the plant?
Question five. Does nectar protect the plant?
Question six. Do non-flowering plants such as ferns make nectar?
Question seven. With floral nectaries, where are most located?
Now, that was not too difficult. The answers are in the script, so no need to send in your responses for me to mark.
Nectar is a sweet exudation from a plant. Not all flowering plants do produce it, for example wind pollinated plants often lack nectaries, as do magnolias and conifers. Surprisingly, the fluid can be produced anywhere – flowers, leaves, stems and even, it is said, roots. Other similar structures can produce oils, for example in Lavandula and Mediterranean species, and insect attracting scents.
The base of the stamens are the most likely location for them in a cabbage-family flower, although they occur at the base of sepals, petals and carpels.
Nectar is a sweet carbohydrate mixture with the main ingredient, apart from water, sucrose (Common table sugar) although small quantities of glucose, fructose and traces of protein may be present. The stomach enzymes of honeybees converts the sucrose to glucose and fructose (A mixture often termed invert sugar). So, nectar and honey are different in that the chemical composition is revered.
Nectar is made in epidermal (surface layer) cells and pushed out through modified stomata. Production can be stimulated by the vibrations caused by foraging insects, land mammals or bats.
Nectar-filled spurs are found in many orchids and only accessed by long-tounged insects.
Floral nectaries co-evolved with insects. Larval stages of many flies and butterflies require body-building proteins and fats to grow. Once mature most do not grow or live long lives, so they only need energy supplies, and these can come from the sugars secreted by plants. Baby butterflies often eat plants, adults take nectar.
Here, at Forest Edge, many of the larger bumblebees cannot squeeze into flowers and access the nectar, so cut holes and rob the plant without dispersing the pollen. Their problem is that the tongue lengths of bee species varies, so are not suited to all flower designs … so cheat! We have honeybees, bumbles and solitary bees such as Davies’ mining bees, also the miniscule common masked bee that is only 5mm long and nests in holes in wood. Physostegia is the common masked bees’ favourite flower.
I’m sure you have noted that bees do not spend their time in a single bloom, but constantly go from one to the next. This is clever plant behaviour, delivering miniscule quantities that takes time to restock – so enhancing the chance of pollen transfer.
To my surprise I found that ferns produce nectar. They, like plenty of other flowering plants, use the free sugars to attract insects that remove insect parasites from them. One African acacia grows holed galls in which nectar is produced and the ants nest. When animals browse the plant, the ants rush out to sting the opposition.
The guttation seen especially well in tropical (house) orchids is a type of nectar secretion. Pitcher plants produce the chemical below the lip to encourage risky insect behaviour and the sticky glue of sundews could be produced by modified nectary cells.