THE VESSELS. 43 



tlieii" respective arrangement, form either the romid 

 cellular tissue, or the elongated cellules, or the cellules 

 disposed necklace-like {en chapelet) ; that in this last 

 state, the dilatation of the vesicles always continuing, the 

 diaphragms break, and change the series of necklace-like 

 cellules into dotted vessels, into false tracheae {fausses 

 trachees), and into true tracheae, according to the degree 

 of development. By this system, Treviranus explains 

 how all the parts of a plant seem to derive their origin 

 from the cellular tissue. 



Kieser gives an entirely different opinion : he refers 

 all this organization to an elastic fibre. When it is rolled 

 spirally, it forms the trachea; when it is disposed in 

 circular or parallel rings, it forms the striped or annular 

 vessels ; when the spires or rings are joined by a porous 

 membrane, the result is the formation of dotted vessels ; 

 when these dotted vessels have their origin in the arti- 

 culations, they are contracted at mtervals, thus forming 

 strangulated or necklace-like vessels {vaisseaux en cha- 

 pelet) ; lastly, when the spires or rings are remote from 

 one another, detached, or united in different degrees, 

 the formation of reticulated vessels results. 



I purposely pass over several other theories, which 

 agree in different points with those which I have rapidly 

 sketched out : an historical narrative of this subject may 

 be found in Kieser's Memoire sur r Organisation des 

 Plantes. What I have said is sufficient to show the 

 extreme diversity of opinion entertained by anatomists, 

 and the almost impossibility of having, in the present 

 state of things, a satisfactory opinion upon points so 

 refined. 



The only idea which appears common to all these 

 theories is, that all the different orders of vessels have 

 the most intimate mutual relations, and can only be con- 

 sidered as modifications of one another; an opinion 



