Fig. 129 Galaxaura. Left, G. marginata ( x 3) ; middle, assimilators 

 of G. marginata ( x 200) ; right, assimilators of G. lapidescens ( x 160). 



(After Borgesen.) 



Other Nemalionales that it may be necessary to remove the genus 

 to a separate order. Liagora tetrasporifera, Helminthocladia hudsoni 

 and Galaxaura do, however, show how the sporophyte may have 

 been intercalated into the Ufe cycle. 



Gelidiales 



This is a small but relatively imiform order. The thallus is more 

 compact than in most of the NemaHonales and all members are uni- 

 axial in construction. True auxiliary cells are absent but special 

 nutritive cells are formed in association with the carpogonia. The 

 order contains plants that provide the best sources of agar-agar in 

 the world (see pp. 447, 451). 



Gelidiaceae: G^/ZJ/mw (congealed). Fig. 130 



The stiff, cartilaginous thallus, which is often pinnately branched, 

 is based primarily upon the imiaxial type of construction. This is 

 most clearly seen at the apex, but in the older parts of the thallus it 

 is converted to a central portion of large cells, derived from four 



234 



