lo Johnstone, Calamites i^Calaviitind) varzans, Sternb. 



referred to below, no generalisation as to occurrence and 

 function has been arrived at. 



Williamson (4) mentions two Calamites, in one of 

 which every 5th internode is short, and in the other every 

 8th. He expresses his inability to correlate these varia- 

 tions with any known external features, but suggests the 

 possibility of their being of specific character. 



Stur (5) figures several most instructive examples of 

 Calamites, but does not enter into discussion of the 

 grouping of internodes. Some of the figures, as placed, 

 are inverted, but the true lower boundary is quite clearly 

 indicated in some of them by the subtending leaf-bases, 

 in others by the direction of growth of the younger 

 branches. Amongst those which may be relied on as 

 evidence to show whether short internodes lie above or 

 below the whorl of leaf-scars, are those quoted below. 

 PL W.^Fig. 4, is clearly inverted ; PI. W., Fig. 5, is almost 

 certainly in the same position ; PI. II., Fig. 3, is correctly 

 placed; PL V. and PL XI. are specially valuable. In 

 these the branch bearing the whorls of branch scars is 

 itself still in connection with an older axis : we can thus 

 be quite certain about the relative positions of its parts. 

 In all of the above, without exception, the abbreviation of 

 internodes appears either in the internode in which the 

 scars lie or in those above it: the internode below is 

 always comparatively long. Reference is made to them 

 as affording confirmation of the opinion as to which is 

 top and which is bottom of the Bradford specimen. 



Incidentally the last two specimens also illustrate the 

 fact that the same plant bore its smaller branches or 

 twigs in whorls, whilst the larger branches were sparsely 

 and irregularly scattered over the parent axis. That is 

 to say, Calamitina and Styocalamites might represent 

 different orders of branching in a single plant rather than 

 different groups of species. 



