ORGANOGRAPHY. 



])ut slight modifications of reticulated vessels ; but in their more 

 perfect state, scalariform vessels assume a prismatic form, as 

 in Ferns {fiy. 70), of which they are then especially character- 

 istic. 



The annular, reticulated, and scalariform vessels have commonly 

 tapering points like the true spiral vessels, and thus overlap at 

 their extremities when they come in contact {fig. 70), in which 

 case they appear to be nothing more than elongated tubular 

 cells. In some other instances they terminate more or less 

 obliquely, or by flattened ends, as if forn^cd of rows of cells like 

 most pitted vessels, and that this is their real origin in such cases 

 is proved also by the occurrence occasionally of contractions 

 on the sides of their walls, so that tliey assume a beaded ap- 

 pearance, such contractions indicating the points where the 

 component cells come in contact (Jiys. 66 and 71). In rare 

 instances the true spiral vessels also present similar contrac- 

 tions on their walls. 



These vessels are but slight modifications of the true spiral. 

 This is proved by the fact that we frequently find in the 

 same vessel one or more of the above forms 

 combined with the spiral {figs. 68 and 72), 

 and thus forming intermediate states of 

 each other. According to Schleiden and 

 others, they are not only slight modifica- 

 tions of spiral vessels, but are actually pro- 

 duced from them in consequence of certain 

 alterations which take place in the course 

 of their development. Thus, annular vessels 

 according to this view, are formed by the 

 growing together of portions of the origi- 

 nal spiral fibre into rings, the intermediate 

 portions between such rings becoming ulti- 

 mately absorbed, lleticulated and scalari- 

 form vessels again, are said to be formed by 

 the formation of cross fibres in various directions between the 

 ct)ils of tlie spiral fibre, so that the s]Mral is converted into 

 u reticulated or scalariform vessel. Other obsen^ers, espe- 

 cially Mulil, state positively that tliere is no change produced 

 in the condition of tlie fibre within these vessels by age, but 

 that it is always deposited originally in the same condition 

 which it ultimately assumes, and that the seeming transitional 

 stages from spiral vessels into annular and reticulated, .are per- 

 manent intermediate forms l)otween them. The first view, that 

 whicli lias l)ecn so ably advocated by Schleiden, seems to me 

 to be most in accordance with the ])osition and ordinary appear- 

 ances presented by them rcsjx'ctively. 



f. Latirifcrous Vessels or YV.v.sMt'.— These constitute the MiVA- 

 vessels of the old authors. Tliey consist of long branched tubes 



