This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Hemlock, in spite of its poisonous nature, is widely distributed, being found (to-day) throughout the North Temperate Zone, in Europe, N. Africa, Siberia, and it has been introduced in N. America. It is general in Great Britain, but is not found in Cardigan, S.E. Yorks, Main Argyle, Mid and N. Ebudes, W. Ross, E. Ross, Shetlands. In Yorks it ascends to nearly 1000 ft.
It is a moisture-loving plant, usually growing by the sides of streams and rivers, or away from such spots along the roadside, occasionally outside outhouses, and very rarely on the borders of cornfields. Its present distribution may be partly artificial owing to its poisonous properties, its ill effects leading in some instances to extermination. Cattle generally avoid it. As is well known poisonous plants have usually some warning-signals which enable animals to avoid them, and in this case the foetid smell is accompanied by a purple spotting of the stem (at once a suspicious novelty), which is further covered with a blue powder.
The Hemlock is very tall, graceful, erect, bearing- numerous branches. The stem is smooth, bluish-white, shiny, hollow, and finely furrowed. The leaves at the base are large, triangular, shining, very much divided, the oblong leaflets having sharp coarse teeth. When crushed, the leaves smell like mice.
The umbels of the flowerhead are terminal, those of the partial involucres or whorls of leaflike organs on one side only lance-shaped. The flowers are small, numerous (several hundreds in one umbel), and so conspicuous. They are white, and the first ones to open are male flowers. There are no calyx teeth.
The petals have a turned-in point serving to protect the honey, and are blunt, heart-shaped, and unequal. The umbels are axillary. The flowers are sweet-scented.
The Hemlock grows to a height of 5-10 ft. The flowers open in June and July. It is perennial, and reproduced by seeds. In winter the roots contract, and the plant is drawn down into the earth.
The flowers mature slowly and gradually, and at first are entirely male, and later entirely female. When the flower opens, the anthers open, and are covered with pollen one by one before the styles appear. Each anther is at a distance of two-fifths the circumference from the preceding one. The anthers elongate and stand above the stigma. In the middle of the male period the older anthers wither and turn outwards, while the rest are opening and take their place, and are covered with pollen. The styles are still short and bent in with the stigmas unripe. After all the anthers have fallen off, the styles become erect, and stigmatic knobs form at the end of the styles.
The flowers are visited by Sargus, Calliphora, Lucilia, Scatophaga, Meligethes, Trichius, Nematus, Ichneumonids, Pompilus, Andrena. The fruits are flattened or winged to aid in their dispersal by the wind, and are when ripe but slightly attached, so that a gust of wind blows them away, or they are dispersed by a jerk from passing animals.
Photo. W. E. Mayes - Hemlock (conium Maculatum, L.)