Frogs and Toads
Frogs emerge from hibernation this month, returning to water to breed. Look for the jelly-like frogspawn in ponds, ditches and slow-moving water. Observations have suggested that this is appearing earlier in the year than in the past, possibly as a result of global warming. If you can, please help increase our knowledge of the current time of spawning by looking for frogspawn and entering your records on the Phenology website, www.phenology.org.uk/springintoscience.
Frogs breed before toads, which emerge from hibernation slightly later and lay their eggs around water plants, in ribbon-like strands 2-3 metres in length. They need deeper, better oxygenated water than frogs, so look for them in or near bigger ponds. Warm, moist air triggers adult toads to emerge from hibernation and travel to breeding ponds which the smaller males usually reach before the females. They often wait near the ponds to find a female before entering the water. As with frogs, toads are generally more active at night, males croak to attract females and cling to the back of the females to fertilise the eggs (spawn) as they are laid.
Mistletoe - download Life Cycle sheet: www.bromley.org/ciswebpl/darwin2/docs_pdfs/mistletoe.pdf
Darwin studied mistletoe and wrote in the introduction to the Origin of Species how important he felt it was to try to understand by what means plants such as mistletoe could have become adapted to survive. The life history of mistletoe is so complicated because, as a semi-parasite this plant relies on its host (often apple trees, sometimes lime, hawthorn or poplar) for water and mineral salts, relies on birds to disperse its seeds and has flowers with separate sexes on separate plants and therefore needs insects to pollinate it.
With the loss of apple orchards which were once more common in the nominated World Heritage Site, mistletoe had disappeared but was reintroduced in February 2006. Mistletoe is a London Biodiversity Action Plan species, for more information see: www.mistletoe.org.uk
Look for hazel catkins this month and the small red female flowers borne on the same branches (see photo). Well adapted for pollination by the wind, the long male catkins blow about releasing large quantities of pollen. When it lands on a female flower a tube grows from the pollen grain towards the base of the style but then stops because the female part of the flower (the ovary with the ovule within it) is not ready for fertilisation until July. After fertilisation the nut develops and ripens by late August. In the The Different Forms of Flowers on Plants of the Same Species, published in 1877, Darwin wrote about plants which have their sexes separated but borne on the same plant (monoecious species):
"The flowers necessarily differ, but when those of one sex include rudiments of the other sex, the difference between the two kinds is usually not great. When the difference is great, as we see in catkin-bearing plants, this depends largely on many of the species …being fertilised by the aid of the wind; for the male flowers have in this case to produce a surprising amount of incoherent pollen."
He also wrote about how the different male and female flowering times helped to ensure cross fertilisation in hazel. Before Darwin wrote about these things most people believed flowers were just decorative and plants fertilised themselves.