THE SOLID COMPONENTS OF PLANTS. 231 



oily secretions. They are found in greatest numbers in 

 the less compact woody parts of the plant. The centre 

 of the majority of the species of Lycopodum, or Club- 

 moss, contains a thick cylinder, which is chiefly com- 

 posed of vessels of this kind. Ferns also inclose 

 many of them, in their woody threads; and several 

 other plants, particularly the Vine, the wood of which 

 is soft and porous, and contains them in great num- 

 bers. 



Each of these species of perforated vessels is occa- 

 sionally seen forming different parts of the same tube ; 

 or one portion of it may present the cribriform charac- 

 ters and another the annular. 



3d. The next set of vessels, the Spiral, have been 

 known to botanists since the time of Grew, who was 

 the first that gave his attention to the anatomy of 

 plants. They have been named vasa spiralia, and 

 jissurce spirales from their appearance ; and trachece, 

 from their resembling the tracheae of insects, and 

 from an unfounded opinion that they were the vegeta- 

 ble organs of respiration. They are the largest of the 

 vegetable vessels ; and in many plants their structure 

 is visible to the naked eye. Thus, if a leaf, or a green 

 twig of Elder (Sambiicus canadensis), the petiole or 

 peduncle of the Water Lily, or the stem of the com- 

 mon Lilies, or the leaves of various species of 

 Amaryllis, when on the decay, or the fleshy scales of 

 any bulb be partially cut, then cautiously broken, and 

 the divided portions carefully drawn asunder, the spi- 

 ral vessels will be seen appearing like a screw, and 

 their real structure become apparent. They are form- 

 ed of a thread, turned in a spiral manner from right 

 to left ; as if a fine slender and flattened wire were 

 w T rapped round a small cylinder of wood, so that the 

 successive rings touch each other, and then the cylin- 

 der be withdrawn ; the form thus acquired by the 



