The content for this section was produced by Eddie Aicken BSc (Hons) Biological Imaging who produced this web site as part of BSc (Hons) degree in Biological Imaging, at the University of Derby. This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Eddie graduated in June 1997 and is now working as a medical photographer.

Introduction

Over time, many plants have adapted their structure and their flowers to be more readily pollinated by insects. The more successful ones survived and continue to evolve to their pollinators needs. The results are flowers which are often brightly coloured and/or scented to advertise the availability of nectar. The nectar is the motivating factor for the potential pollinator to visit the plant. The nectar is placed to ensure that the insect brushes past the pollen or the anthers, increasing the chances of pollination as they feed. It is then no surprise to note that insects behavioural patterns and visual systems are exploited by plants. This is seen in the visual cues, which flowers provide, for the insect to close in on the nectar.

There are two main ways in which the flower can provide visual cues. The first is the use of lines of contrast converging on the nectar containing region (Nectar guides see Biology page). The Thistle,Cirsium vulgare (Fig.1, right), is a good example of this, it is a roundish flower with dark lines pointing towards the centre, regardless of the direction of approach. The other type of visual cue, referred to as the "bulls eye effect", is a dark area in the centre of the flower. A common example of this is the Michaelmas Daisy, Aster novae-belgii (Fig.2, right), which also has lines on the petals leading towards the bulls eye.

These visual cues are intended for the eyes of pollinators, which can see ultraviolet light, as well as other colours. Ultraviolet patterns are invisible to most animals including humans, they often mirror patterns which we can see. They also occur on plain, apparently patternless, flowers.

Fig.1 Common Thistle - Cirsium vulgare