144 VEGETABLE SUBSTANCES. 



is formed, they destroy the chrysalis by means ot 

 heat. 



Previous to the time when the two missionaries 

 brought the eggs of the silk-worm from China, and 

 succeeded in obtaining raw silk at Constantinople, 

 silk was a very costly article, the price in Rome being 

 an equal weight of gold. But the number of worms 

 augmented rapidly, and Greece, more especially the 

 Morea, produced an abundant supply. The conquest 

 of Constantinople by the Venetians, in 1204, led to 

 the introduction of the article into Venice, from 

 which, in the course of a short time, it extended to 

 Genoa, and other parts of Italy. Henry IV. was 

 anxious to introduce the silk-worm into France, and 

 he took some very efficient measures to advance that 

 object; but his success was not equal to his wish. 

 Colbert, in the reign of Louis XIV., was the first 

 who added it to the productive wealth of that country, 

 upon a large scale. James I. was desirous of intro- 

 ducing it into England, and there have been many 

 trials since; but, though these have promised to be 

 successful, they have not been prosecuted, probably 

 because the culture is better adapted to warmer skies 

 and a less laborious population. When the mulberry 

 is cultivated for the rearing of silk-worms, it is not 

 allowed to grow to a timber-tree. The young shoots 

 are preferred for that purpose ; and, therefore, in 

 China, the trees are either cut down altogether every 

 third year, or they are kept low by pruning. When 

 the leaves of the mulberry fail, or are deficient, in 

 China, those of the ash are said to make no bad sub- 

 stitute. Some varieties of the ash have certainly this 

 much in common with the mulberry, that they do 

 not expand their leaves till the season be far ad- 

 vanced, seldom till the middle of May, and very 

 often not till the end of that month. It is stated 

 that the Chinese dry the mulberry leaves in the sun, 



