118 BRITISH FLOWERING PLANTS chap. 



night and in wet weather. The capsules open by ten 

 longitudinal slits, the lignified part being thinner and 

 less compact along the lines of dehiscence. 



L. catharticum. — The anthers and stigma are about 

 at the same height ; but at first the stamens are curved 

 outwards. As, however, they gradually turn inwards, 

 and, moreover, as the flower closes at night if it rains, it 

 can easily fertilise itself. The stem is quadrangular ; the 

 lower leaves are opposite, the upper alternate. 



L. usitatissimum (Common Flax). — An annual, with 

 erect stem and alternate leaves. The sepals are pointed. 

 The flowers are much larger, and of a beautiful blue, 

 but in structure resemble those of the preceding species. 

 They are visited by butterflies and moths, humble bees, 

 and bees, as well as flies. The value of flax fibres for 

 thread is mainly due to the "bast" fibres, the cells of 

 which attain the unusual length of 20-40 mm. They 

 are, moreover, as strong as iron. 



L. angustifolium. — Like the preceding, but sometimes 

 perennial ; decumbent in habit, and with smaller flowers. 



L. perenne. — A perennial, with alternate leaves. The 

 sepals are obtuse, the petals large, but not so large as 

 in the Common Flax. The flowers are dimorphous, as 

 in the case of the Cowslip and Primrose ; that is to 

 say, the anthers are in some flowers above the stigma, 

 while in others the stigma is above the anthers. The 

 two forms never occur on the same stock, and the 

 object is to ensure cross - fertilisation ; insects carrying 

 the pollen from the long -styled flowers to the short- 

 styled, and vice versa. Darwin,^ since confirmed by 

 Hildebrand, has shown that the long -styled form is 

 sterile, and the short-styled nearly sterile, to pollen of 

 its own form. In the long -styled forms the stigmas 

 first face inwards ; but as the insect must insert its 

 proboscis outside the ring of broad filaments, it would 

 not touch the stigma. Subsequently, however, the 

 stigma turns itself round, and thus faces and touches 

 the proboscis. 



^ Darwin, Forms of Flowers. 



