44 li. HILLIS-COLINVAUX 



thin slice of a bit of surface from about the centre of a segment. Place 

 it in a drop of water on a slide making certain the outer surface is 

 outermost, decalcify with 20% hydrochloric acid, drain excess acid with 

 a tissue and refloat in water. The preparation is ready for examining 

 with a compound microscope. 



(iii) For inner utricles and development of cortex. Much of this 

 information can be obtained from the same sections prepared for nodal 

 examination if the rectangular strip removed extends sufficiently 

 deeply in the segment below the node sampled. However, if a nodal 

 sample was not made, cut a similarly shaped piece, oriented along the 

 same axis, from slightly above the centre of the selected segment. 

 Section and prepare according to the instructions for nodal preparation. 



(c) Pattern of medullary filaments at the node. The character of 

 medullary filament pattern at the node was referred to at some length 

 in Section II because it is essentially the only character used by 

 Barton (1901) in her taxonomy. The discussion herein involves their 

 interpretation and use in modern Halimeda taxonomy. 

 The three patterns Barton recognized are : 



the filaments all fuse together in a single unit for a short distance 

 (about 1-1-5 times the diameter of the filament) and then separate; 

 openings, pits or pores develop in the walls between adjacent 

 filaments ; 



filaments fuse for a short distance in pairs and then separate ; 



filaments fuse completely in twos or threes and do not separate 

 therafter (although the filaments continue their branching pattern). 



With Yamada's (1941) new species a fourth category was needed: 

 filaments remain separate throughout the node. 



A fifth type (Colinvaux and Graham, 1964) has been added: 



node composed of a single filament. 



Until the discovery of cryptica all known species of Halimeda were 

 multiaxial, that is they possessed a core of medullary filaments. Species 

 with this fifth pattern of nodal filaments are uniaxial. 



The study of nodal anatomy can be as tedious and difficult as 

 Taylor (1950) understandingly writes, and it should not be surprising 

 that the structure one is seeking to unravel is not always clear cut. 

 Since Barton's publication in 1901, many hundreds of Halimedae have 

 been examined, and many new species recognized. The effect has been 

 not only to add new categories of nodal pattern, but also to extend or 

 modify the definition of patterns already recognized. 



