136 LETTER XXXVIII. 



more probable that in reality its peculiarity is simply 

 owing to the projection of a short plate from the back 

 into the cavity of each cell. 



Common Flax (Linum usitatissimum), as its name 

 imports, is the plant from which linen is manufactured. 

 Its stems are soaked for a long while in water, until the 

 cellular substance rots away, and then the tough fibres 

 that remain behind are cleaned, dressed, and converted 

 into linen thread. You are doubtless aware of the 

 great superiority of linen over cotton thread, in regard 

 to durability and toughness. This is owing to the 

 different nature of the organized substance from which 

 they are prepared. The part of the Flax that remains 

 after maceration is its woody tubes, the toughest and 

 strongest part of the vegetable fabric, and that to 

 which all plants owe their flexibility and strength. It 

 is the part which enables the leaf to bear the violence 

 of the storm without injury, which gives its value to 

 timber, and which enables the cane and the lancewood 

 to bend so freely without breaking. Cotton, on the 

 contrary, is merely the hair that grows upon the 

 seed of the Cotton plant, and is a form of that cel- 

 lular substance which constitutes the parenchyma of 

 leaves, the delicacy of flowers, and the pulpiness of 

 fruit, which fills up the interstices between the woody 

 tubes, and holds together the sinewy framework of 

 vegetation. 



Garden Rue (Ruta graveolens, Plate XXXIX. 2.) 

 is the type of a very extensive natural group, called, 

 after it, the Rue Tribe. It consists of plants having 



