69 



chlorophyll; but tliis is concealed by a brown (" phycophoein "), 

 and a yellow (" phycoxanthin ") colouring material, and hence all 

 these Algae are a lighter or darker yellow-brown. Starch is not 

 formed. Asexual reproduction takes place, (1) by zoospores 

 which arise in unilocular zoosporangia, and are raonosymmetric, 

 with two cilia attached laterally at the base of the colourless 

 anterior end (Fig. 65), the longer one being directed forwards 

 and the shorter backwards ; or (2) by aplanospores (?). 



Sexnal reproduction has only been discovered in a few cases, and 

 takes place by means of gametes (oogamous fertilisation perhaps 



FIG. 66. Ectocarpus tiliaulosug. I a-f 

 A female gamete in the various stages 

 of coming to rest. II A motionless 

 female gamete surrounded by male 

 gametes. Ill a^e Stages in the coal- 

 escence of male and female gametes. 



PIG. 67. Zttiiardim'a collavis. A Male 

 gametangia (the smaller celled) and female 

 gatnetaiigia (the larger celled). C Female 

 gamete. D Male gamete. JJ, E Fertilisation. 

 F Zygote. G Germinating zygote. 



occurs in the Tilopteridse). The gametes have the same structure 

 as the zoospores, and arise in multilocular gametangia ; these, like 

 the zoosporangia, are outgrowths from the external surface, or 

 arise as modifications from it. The conjugating gametes may be 

 similar {e.g. Ectocarpus pusillus), or there may be a more or less 

 pronounced difference of sex, an indication of which is found in 

 Ectocarpus siliculosus (Fig. 60). When the gametes in this 

 species have swarmed for a time, some, which are generally larger, 



