14 Johnstone, Calaviites {^Calaniitina)varians, Stertib. 



(or E). " The most striking feature is the uniform length 

 {i'6 to TQcms.) diwd position of the short internode at the 

 commenceinent of each period. . . . Node A (the short 

 internode) appears to serve the purpose of imparting 

 additional strength to the stem owing to the weight of 

 the branches above," This may mean that the required 

 mechanical support was provided four or five internodes 

 lower down than the node where the branching actually 

 occurred. But it is also open to the interpretation that 

 the branch node is regarded as being situated imme- 

 diately above the short strengthening internode. This 

 last idea seems to be in Mr. Howard's mind when he 

 refers for comparison to Dr. Kidston's specimen (7) and 

 remarks of it: " In length it is 32 1-50 mm., and contains 

 two complete and three incomplete periods, with forty 

 internodes, and a short internode precedes each branch- 

 bearing node'' This statement does not seem to agree 

 with the table of measurements ; the internode below 

 each line of scars is certainly slightly reduced as com- 

 pared with that on which it rests, but the markedly short 

 sections lie immediately above the scar. The conclusion 

 arrived at by Mr. Horwood is that the shortening of the 

 internode precedes a new period of the plant's develop- 

 ment, and that " its function appears to be to add 

 strength to the stem by the occurrence of two con- 

 secutive strengthening nodes (with diaphragms) serving 

 the purpose of a double support within a short distance." 



Inferences. 



It seems justifiable to accept the following facts as 

 established by comparison of the Bradford specimen and 

 the figures of Williamson, Stur, Kidston, and Zeiller : — 



{a) That in certain species of Calamites, or in certain 

 parts of individual Calamites, a recurrent cycle of inter- 

 nodes was correlated with the occurrence of whorls of 



