THE VESSELS. 47 



of them in his Elemens, PI. 10, fig. 9. Kieser adopts the 

 same opinion, at least with regard to the reticulated 

 vessels ; and represents them ramified ( Memoir e Org., 

 PI. 11, fig. 51 ; and PI. 12, figs. 56, 57 j, but respecting 

 the other kinds he does not say it is the case ; however, 

 he appears not to doubt the possibility of this ramifi- 

 cation. It is certain that it is very rare : if it really 

 does occur, it is perhaps only in the articulations ; and 

 as this is the part in plants where the usual interlace- 

 ment of the fibres renders the observation very difficult, 

 there remains some doubt about those ramifications, 

 which, however, probably do exist. Still, even in ad- 

 mitting the appearances represented by Kjeser, must we 

 not well distinguish whether he does not reaUy examine 

 new vessels which are united with the old, or vessels 

 which, being enclosed in one sheath, tend to diverge at 

 their exit ? 



3d. Do the dijlferent kinds of vessels which we have 

 enumerated preserve the same form during the ivhole 

 period of their existence ? 



If the same tube could be examined at different 

 periods of its existence, this question would be sus- 

 ceptible of solution in a direct manner ; but as this 

 observation is impossible, we must have recourse to other 

 means of solving it. 



Those who think that the trachea is the origmal form 

 of all the other vessels, rest their theory upon facts 

 striking enough — viz. that tracheae exist, both in young 

 plants and young shoots, more abundantly in proportion 

 than other vessels ; and consequently it is probable that 

 these other vessels are no more than transformed tra- 

 cheae. Kieser, in particidar, has given great weight to 

 this opinion by his dissections of the Gourd at different 

 ages. In admitting the truth of the fact, we nevertheless 

 cannot deny that there are others quite as positively 



