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1754 A TEXTBOOK OF THEORETICAL BOTANY ,| 



produced in the axil of a bract which is membranous and may be persistent. 



The calyx is absent or may be represented by a small disc or by two 

 glandular scales. There is no corolla present. i 



The androecium (Fig. 1633) in the male flower consists of two or f 

 more stamens each consisting of a slender fllament and a bilocular anther 

 which opens lengthwise. 



The gynoecium in the female flower consists of a sessile ovary which is 

 unilocular and composed of two carpels with two to four parietal placentas. 

 The style is either bifid or tetrafid. The ovules are numerous and 

 anatropous. 



The fruit is a capsule which opens by two to four valves. The seeds 

 are numerous and very small. Each is provided with a cluster of fine hairs, 

 arising from the funicle, which envelop the seed and form a dispersal 

 mechanism. There is no endosperm and the embryo is straight. 



The family is a small one, containing two genera and about 180 species, 

 which are widely distributed in the north temperate, subtropical and 

 tropical regions. There are only two genera, Salix and Popidus. 



One of the constant features of the genus Salix is the origin of the cork 

 cambium from the epidermis. This contrasts with the condition in 

 Populus, where it arises from the hypodermis. „ 



The pollination mechanism in the genus Salix is entomophilous, half- * 

 concealed nectar being present in the female flower, but this mechanism is 

 the simplest found among insect-pollinated plants. The flowers are indivi- ^ 

 dually insignificant but by aggregation into catkins they become quite : 



striking in appearance and are conspicuous objects on the bare trees in ^ 



early spring. The male catkins with their bright yellow stamens are more 

 noticeable than the female and will therefore be visited first by insects. On 

 the other hand more nectar is secreted by the female flowers than by the 

 male and hence these will be more carefully sought for. The combination 

 of these two factors and the fact that few other flowers are open so early in 

 the year, ensure a cross-pollination by numerous insects, including bees. 

 Most of the species of Salix are interfertile and very many hybrids have 

 been produced as a result of cross-pollination. Polyploidy is also a 

 characteristic of the genus. d 



Members of this genus root remarkably readily from stem cuttings. 

 Twigs put in a jug of water will soon form roots, while larger branches, cut 

 and driven into the ground as posts, very soon root and become trees. 

 Willows which line the banks of streams have often originated in this way 

 from posts delimiting fields. Many species are cut down annually to provide 

 young pliable shoots, called "withies", which are used in basket-making, 

 others are allowed to grow and the wood employed in carpentry. Cricket 

 bats are made from selected timbers of Salix coeriilea. Along rivers the 

 Willows are often pollarded, or cut off some 10 ft. above the ground. From 

 the callus formed over the wound a crop of young shoots soon grows out, 

 forming a bushy head. Dust and leaves accumulate among the branches, 

 forming a nidus in which eventually a variety of plants grows : Hawthorns, 



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