The four sepals are a dark purple colour, and they form a cup in which the lower or strap-shaped part of the petal is held.
Those flowers which are nearest the foot of the stem open first. You will often find eight or ten yellow flowers blooming at the same time and a bunch of dark purple buds at the end of the stem.
The stem of the Wallflower is tough and woody near the ground, but further up it is green and smooth.
The leaves are narrow pointed straps with smooth edges. They are dark green, but sometimes they have a touch of purple at the tips.
2. WILD MUSTARD
This is a plant the farmers are very sorry to see. They do not want it among the corn, but in springtime the fields are often covered with its yellow flowers.
The flowers grow in a cluster near the top of the stem. There are often four or five in full bloom at once, gathered round a bunch of green buds which rises in the centre of the cluster. While the first cluster is in flower, the stem continues to grow, and by the time these flowers fall off, another cluster appears at the end of the lengthened stem, and so on.
If you pull off one of the flower-petals you will see that the lower half is strap-shaped. But the petal is much broader at the other end, and it is round, with a tiny nick in the outer edge.
In the centre there are six stamens whose tips you can just see where the four petals meet. But the seed-vessel is hidden until the petals and sepals and stamens fall off. It then grows into a thin green pod, and you will find many of these slender pods standing out from the hairy stem.
Behind the yellow petals are four thin sepals. When the flower is fully out these lie flat open. They do not form a cup.