ON THE BRITISH SPECIES OP OEISIA. 137 



method of branching is well developed, the internodes compos- 

 ing the sympode are usually made up of five zooecia, and that, 

 although the branching may, in other parts of the colony, take 

 place from z^ (or rarely from z^ or z^, well-developed helicoid 

 cymes are invariably composed of internodes in which the 

 branching takes place from z^. 



These helicoid cymes do not, however, agree with the method 

 of branching defined under that term in text-books of botany, 

 in that the main axes of the parts of the sympode are by no 

 means suppressed. This is obvious enough from the formula, 

 in which the first internode on the left side forms the basal 

 member of a helicoid cyme developed on the left side of the 

 branch ; but it is, at the same time, the basal member of a 

 long axis, which develops new cymes alternately on opposite 

 sides ; and the same is true of the other constituents of the 

 sympodes. Thus each of the branches indicated in the formula, 

 with the exception of those which are quite near to the grow- 

 ing-points, is again the basal member of a helicoid cyme ; and 

 these cymes are consequently given off alternately on opposite 

 sides, not only by the internodes of the main stem, but 

 also by the internodes of its branches of the second, third, 

 and other orders. The number of members of which these 

 helicoid cymes are composed decreases fairly regularly in a 

 centrifugal direction. 



Each internode is typically provided with one branch, and 

 at the same time is composed of an odd number of zooecia, 

 just as in C. denticulata. It is not uncommon, however, to 

 find branchless internodes, whose position in the colony may 

 be illustrated by the formula— 



(5 -I- n) + (6) H- (5 -h !»•); 



and, just as in C. denticulata, these branchless internodes 

 nearly always consist of an even number of zooecia, most 

 commonly of four or six, less often of two or eight. Ex- 

 ceptions to this rule are somewhat less rare than in C. den- 

 ticulata, which this species so closely resembles in its method 

 of branching. The exceptions are more common at the base 



