S2 VEGETABLE ORGANOGRAPHY. 



US remember that this tube has only been seen by a 

 small number of observers, and that Hedwig himself 

 seems less to have seen it, than to have conceived it in 

 theory ; for notwithstanding his skill as a draughtsman, 

 he has not ventured to give a dra^ving of it. Link 

 says that the observation of Hedwig has not been con- 

 firmed by any anatomist ; and, for my part, I do not 

 deny this assertion. Mirbel assures us that, in some 

 cases, the old trachese present in the interior a kind of 

 incrustation more or less dense, wliich resembles a true 

 internal tube ; but as this appearance of the interior 

 tube is very rare, one would be authorized in not con- 

 sidering it as an integral part of true tracheae. 



2d. Is the part iv/dck forms the spire flat, as former 

 observers asserted ; or is it a little hollowed into a chan- 

 nel and bordered by a thickened rim, as the figures of 

 Mirbel indicate ; or is it tubular, as Hedioig and Mustel 

 affirm ? 



The greater number of observers are opposed to this 

 last opinion, although several among them have ob- 

 served the tracheae with more powerful glasses than 

 those of Hedwig. Still later, Amici, who makes use 

 of the strongest microscopes known, remains in doubt 

 concerning the tubularity of the tracheae ; and believes 

 that the question cannot be solved by the optical means 

 which we possess. One of the arguments which appears 

 to have persuaded Hedwig to admit the tubular nature 

 of the spiral part, is, that when a coloured liquid rises 

 in these organs, one distinctly sees that it follows the 

 spire ; but this appearance is as easily explained by 

 admitting that it is a band a little concave, along w^hich 

 the coloured liquid glides, as in supposing it to be a 

 perfect tube. Nevertheless, the hollow form of the band, 

 or the existence of the rims, is still contested by several 

 of the most able observers. Kieser, in particular, 



