LBCT. VII.] ANATOiMY OF STEMS. 359 



mined, the spiral vessels are seen in some instances 

 detached, or not immediately accompanied by any 

 other description of vessels, and in others they are 

 accompanied by either cribriform or annular ves- 

 sels according as the one or other of these are the 

 common vessels of the alburnum and wood. Thus, 

 in longitudinal and in tangental sections of the 

 medullary sheath of the Horse Chesnut, the spi- 

 ral vessels are accompanied with the cribriform 

 vessels only of the wood ; and such is, also, the 

 case in the Elder (Sambucus nigra), and in the 

 Lilac (Syringa vulgaris). In the Elastic-gum Fig 

 tree (Ficus elastica), the sheath of which is not dis- 

 tinguishable by colour, the spiral vessels are seen 

 close to that part of the first year ! s wood, which 

 touches the pith, and consequently in the situation 

 of the sheath ; but they are not immediately ac- 

 companied by any other vessels : those nearest to 

 them, however, are cribriform, like the larger 

 vessels of the wood. In the Medlar (Mespilus), 

 in which there is, likewise, no evident medullary 

 sheath, the spiral tubes, which are very numerous, 

 are accompanied by the common vessels only of 

 the alburnum : and in the Cinnamon (Laurus 

 Cinnamomi) the accompanying vessels are annular, 

 such being the vessels of the alburnum and the 

 wood. The cells of the medullary sheath (Plate 

 6, fig. 7, d. e. 8.) are narrow and oblong ; and, 

 therefore, when it is not coloured it is scarcely 



A A4 



