THE YOUNG NATURALIST. 



127 



markets are common in Europe and Asia. At Broasa, great numbers of 

 mules, camels and asses, are freighted with mulberry leaves for the leaf 

 market. 



At the close of the thirteenth century, the celebrated traveller, Marco Polo, 

 in his narrative of travels in the Celestial Empire, says : " No fewer than one 

 thousand carriages and pack horses, loaded with raw silk, make their daily 

 entry into Cambula, where silks of various textures are manufactured to an 

 immense extent. 



In 1761. Savannah, in the United States of America, had a filature and 

 exported to England 8829 pounds of raw silk. In 1775, Mrs. Pinckney, of 

 South Carolina, conveyed enough of American silk to England to make 

 three dresses. In 1790 the last parcel was brought for sale. There has, 

 however, been a revival of sericiculture in the United States of America, 

 and a society exists in Philadelphia, which is managed by ladies, who 

 render valuable assistance by giving instructions in the rearing of silk- 

 worms, and in the reeling of cocoons, as well as distributing young mulberry 

 trees to such persons as are desirous of aspiring to sericiculture. Mulberry 

 trees are extensively cultivated in California, where millions of trees have been 

 planted, and in some instances have realised a profit of £200 per acre. In 

 the report on the Colonial and Indian exhibition, by Mr. Thomas Wardle, of 

 Leek, Staffordshire, is the following : " As an example of the profit to be 

 realised, a Californian fact may be cited, according to which £700 was the 

 clear gain from 2>\ acres, the working expenses having been £93." 



There are many varieties, or perhaps species, of silkworms, which are known 

 under the name of Bombyx mori. Some silkworms are described as black, 

 and others as tiger spotted. The cocoons of the various races differ in 

 structure, and the races, or species, differ in fecundity. B. mori and B. tex- 

 tor produce one brood annually ; B.fortunatus, B. sinensis, and B. arracanen- 

 sis produce several broods annually, while B. crasi produces seven or eight. 



All species of silkworms have two stores of fluid silk on each side of the 

 alimentary canal, and below their mouths they have two seripositors, through 

 which the silk issues simultaneously in pairs of fine filaments, or fibres, form- 

 ing, in fact, a double thread which is coated with gum, and unites both 

 fibres. The structure of the double fibres of the silkworm of Bombyx mori s 

 when cut transversely, is that of two circular discs ; the fibre on the cocoon 

 is uninterrupted, except in those which are formed by two silkworms, which 

 are called double cocoons : the latter are unreelable. 



The cocoons are softened with boiling water, soap, &c, and are then reeled 

 six or eight threads together ; double cocoons and floss, or waste silken fibre, 

 is carded and spun, 



