218 



PRINCIPLES OF PLANT-TERATOLOGY. 



more approximated on one side ; (9) leaves displaced 

 about an inch and the lowest leaf forked so far as the 

 base of the stalk without complete separation into 

 two; (10) leaves nearly opposite, each with an in- 

 florescence in its axil. On another plant a branch 

 representing the stronger of two resulting from a 

 fork, showed the following nodal variations : (1) 

 leaves displaced a quarter of an inch ; (2) a single 

 leaf ; (3) two slightly displaced leaves, not opposite, 

 but approximated on the side opposed to that on which 

 the single leaf of node (2) is situated at a lower level 

 corresponding to the length of a normal internocle ; 

 the leaf of (2) may be regarded as having been con- 

 genially displaced downwards from the position of the 

 widest gap between the two leaves of (3) where it 

 would form with them a whorl of three ; (4) wdiorl of 

 three leaves each separated by a quarter of an inch 

 from the other; (5, 6, and 7) whorls of three leaves; 

 then begins the inflorescence. Also on many shoots, 

 especially the suckers, of Lonicera thibetica the leaves 

 of several whorls (consisting usually of four leaves) 

 were irregularly displaced ; the displacement here is 

 coupled with forking of many of the leaves; it has not 

 proceeded so far but that the scattered leaves can in 

 every case be referred to the whorls they have been 

 displaced from (PI. XX, a). In one branch which bore 

 whorls of three leaves there was one whorl which had 

 two leaves only, not opposite, but widely separated on 

 one side ; the next node below had a whorl of three 

 leaves, one of which was forked, and one of the halves 

 so formed was again forked unequally. The cases 

 taken from these two plants represent a very imperfect 

 and half-hearted transition from the opposite-decussate 

 to the alternate or spiral arrangement. 



The ash (Fraxinus excelsior) frequently exhibits on 

 some of its branches the f phyllotaxis without any 

 trace of the opposite-decussate arrangement. 



Where the change is much more complete and pro- 

 nounced it is accompanied, as the internodes lengthen, 



