Alder pollen. Macrophotograph of pollen falling from the male flowers (catkins) of the Italian alder tree, Alnus cordata, in a light wind. The alder catkins produce yellow, powdery pollen in vast quantities and release it onto the breeze. The wind then carries the pollen to fertilise female flowers. Wind-pollination is a haphazard process and so plants which rely on this form of fertilisation produce vast quantities of pollen. The resulting fine, airborne powder can trigger allergies, known as 'hay fever', in susceptible individuals. Magnification: x1. 5 at 35mm size.