ir6 PHAEOPHYCEAE 



smaller than the mature ova, each of which contains thirty or more 

 chromatophores. 



The oogonia, with which hairs are sometimes associated, are 

 also formed from superficial cells which divide into a stalk cell 

 and an oogonium initial. The ripe oogonium contains sixteen to 

 fifty-six eggs which, after liberation, remain motile for a period of 

 from 5 min. to 2 hours, whilst the antherozoids can remain active 

 for about 20 hours. E)ischarge of the gametes takes place at any 

 time during the day but is at its best about 5 a.m., fertilization 

 taking place in the water when the diploid number of chromosomes 

 (48) is restored. Upon germination a small columnar structure is 

 first formed and then a flat basal expansion grows out from its base 

 to form the adult sporophyte, which is a prostrate expanded thallus 

 attached to the substrate by means of rhizoids. It differs so very 

 much from the gametophyte that w^hen first found it was thought 

 to be a separate genus and was given the name of Aglaozonia. It 

 sometimes happens that the ova do not become fertilized, and when 

 this happens they germinate parthenogenetically to give haploid 

 Aglaozonia plants, but these do not bear any reproductive organs. 

 The sporophytic thallus is composed of large cells in the centre with 

 superficial layers, both top and bottom, of small cells. The sessile 

 unilocular sporangia, sometimes accompanied by deciduous hairs, 

 are borne in palisade-like sori or else are scattered irregularly on the 

 upper surface of the thallus. Each superficial cell first divides into 

 a stalk cell and sporangium initial, then meiosis occurs and 

 eventually eight to thirty-two zoospores are formed in each 

 sporangium. The zoospores on germination give rise to new 

 Cutleria plants. This life cycle was first worked out by Yamanouchi 

 (191 2) for the common species Cutleria multifida and its sporophyte 

 Aglaozonia reptans. 



SPHACELARIALES (ISOGENERATAE) 



The next three tj^'pes belong to the Sphacelariales, an order 

 frequently known as the " Brenntalgen " because they possess a 

 very characteristic large apical cell with dense brown contents, the 

 detailed classification of the group being based primarily upon the 

 behaviour of this apical cell at branch formation. The plants have 

 regular branching and a bilateral symmetry, both of which form 

 characteristic features. Structurally they can be regarded as 



