STRUCTURE.] NODE-FORMATIONS. 233 



I found a uniform mass of wood, formed of prosenchym- 

 atous cells without vessels, among which are scattered small 

 vertical cords of a very delicate parenchym, in the midst of 

 which ran spiral vessels, most of which could be unrolled. 



III. A third matter of importance, arising out of such 

 essential differences in the stem, is the relation of the axis 

 to leaves and buds, with which are connected many striking 

 appearances. 



a. A phenomenon common to all Dicotyledons, is the forma- 

 tion of nodes. The lateral organs (appendages of the axis), 

 in fact, never originate among Dicotyledons at any other 

 place than the nodes, where we find a peculiar arrange- 

 ment of the vascular system which may always be ascer- 

 tained by careful dissection. At such nodes there appear 

 two or more woody bundles which, by being merely placed 

 one on the other, or by anastomosing, form a loop (ansa) 

 and from this plexus the organs of the circumference 

 derive their woody bundles. From this, in connexion 

 with the peculiar form of the medullary rays, arises an 

 infinite variety of woody structure. This loop is more 

 especially intended to connect the parenchym of the 

 lateral organs with the pith or living parenchym of 

 the axis. The size of the loop is essentially dependent 

 on the thickness of the base of the leaves or lateral buds. 

 In Monocotyledons,, this formation of nodes is rare, 

 if indeed it occurs at all ; for I am not sure that a real 

 anastomosis of the vascular system occurs in the so-called 

 nodes of grasses, for the purpose of giving off woody 

 bundles to the lateral organs. This, at least, is certain, 

 that in Monocotyledons the anastomosis of the vascular 

 system is undoubtedly more rare than in Dicotyledons. 

 If we could be sure that the formation of true nodes did 

 not occur amongst Monocotyledons, we should have a 

 fundamental distinction bet ween them and Dicotyledons. 

 In Acotyledons we again find a true dicotyledonous 

 formation, and much needless discussion about the pecu- 

 liarities in the stems of Ferns would have been spared, if 

 the plan of structure from which it is said to deviate, 

 (viz., the dicotyledonous stem) had not been limited 



