Fig. 115 Ascophyllum nodosum. A-C, diagram showing method of 

 branching. A, apical cell. A^-A^, secondary initials in order of 

 development. AA^, AA^, tertiary and quaternary initials. D, plant 

 ( X I). E, microsporangia ( x 225). F, megasporangium ( x 2-25). 

 (A-C, after Oltmanns; D-F, after Newton.) 



SO the number of pneumatocysts may indicate the age of the plant. 

 The axis is beset by simple, clavate, compressed branchlets that 

 arise singly or in groups in the axils of the serrations. These are 

 later converted into or are replaced by short-stalked, yellow, fertile 

 branches which fall off after the gametes have been hberated from 

 their conceptacles. The macrosporangia each give rise to four ova, 

 the remaining four nuclei degenerating. 



The method of branching is perhaps best understood from an 

 inspection of Fig. 115. In spring the main branches divide dicho- 

 tomously as in Fucus, after which opposite pairs of fertile recep- 

 tacles or sterile tufts of hairs are produced in notches that are 

 formed as follows on both sides of the thallus. The apical cell (A) 

 cuts off another apical cell (AO that remains dormant for a time, 



205 



