PERFOLIATE SPRING-BEAUTY— continued. 
sense of having been here before the arrival of man. Besides the intentionally- 
introduced species which we cultivate, whether for food, timber, fibre, medicine, or 
other purposes, several grades have been recognised among aliens , or species 
unintentionally introduced, according to their degree of establishment. Temporary 
introductions, such as many brought in ships’ ballast, or in foreign wool, or escaping 
from gardens, but unable to hold their own, are known as casuals. Weeds of 
cultivated ground, which may be of ancient introduction but do not pass beyond the 
limits of cultivation, such as our Poppies, are termed colonists. On the other hand, 
escapes from cultivation, which, like Claytonia perfoliata , are able to reproduce 
themselves freely and to spread away from cultivation, are known as denizens. 
Claytonia perfoliata grows to a height of from four to twelve inches and has a 
few fleshy rhomboid radical leaves ; while its pairs of cauline leaves — one on each 
stem pair — are united into a sub-orbicular and equally fleshy blade with two slight 
points. The slender inflorescence rising from the centre is a somewhat complex 
sympodial cyme, though appearing like a racemose series of three-flowered whorls. 
Before the small flowers have been pollinated they stand erect. Within the two 
sepals or bracteoles, the five white petals, slightly notched at their tips, rise a little 
higher than the sepals and honey is secreted at the base of each, so as to be accessible 
to any short-tongued insects. The five stamens are opposite to and attached to the 
bases of the petals, and their anthers mature before the stigmas do so. After the 
anther has split and discharged its pollen the filament moves outwards, i.e. farther 
from the centre of the blossom. The superior ovary is surmounted by a three-cleft 
style, and after the pollination of the stigmas the flower-stalk bends downwards 
through about i8o°, bending back once more into the vertical position when 
the seeds are ripened. The globular membranous capsules split, when ripe, into 
three valves, and these as they dry contract so as to throw the three comparatively 
large, black seeds to some little distance. This scattering of the seed is facilitated by 
their position, each lying across the line along which the valves separate, and this 
mechanism is probably the main explanation of the rapidity with which this alien 
species has spread over the country. 
The addition to our flora from time to time of such attractive aliens is some 
compensation for the loss of British species which, from -various causes, are 
exterminated. 
