The Teasel.
We conclude this chapter with a description of the common Teasel (Dipsacus sylvestris) of the order Dipsaceæ. This is really a very graceful plant, rarely less than three or four feet high, and sometimes reaching six feet or more. Its stem is very stout and prickly; and its large bright green leaves are simple, sessile, and arranged in opposite pairs. They are prickly beneath, and the two leaves of each pair are united at their bases in such a manner that they form hollows in which the rain-water collects. The reservoirs so formed often contain drowned insects which have flown or fallen into the water, or which have been washed down the stem by the rain. Their dead bodies decompose, giving rise to nitrogenous and other products of decay which generally discolour the water. These products are valuable as plant food, and it has been said that they are absorbed by the leaves. The flowers of the Teasel are collected in large heads, covered with straight, stiff bristles, and have an involucre of bracts which curve upwards. The flowers are of a pale purple colour. They commence to open near the middle of the head, forming a horizontal circle; and then they expand both upwards and downwards from this level. The flowers are not conspicuous individually, nor does each individual flower produce much pollen; but the large heads of bloom attract numerous insects which climb about among the flowers in search of nectar, covering their bodies with pollen, and thus aiding the process of fertilisation.
Teasel-heads.
1, 2, and 3 are successive flowering stages. 4, The elongated head in fruit.
[XII]
WAYSIDES AND WASTES IN SUMMER (Continued)
Composite Flowers
There are so many flowers of the order Compositæ in bloom by the wayside and on waste ground during the summer months that we devote a chapter entirely to them.