BROWN ALGM 143 



like or fan-shaped fronds, these latter often splitting 

 up into narrow, long pieces. Their reproductive organs 

 are motionless eggs, and mobile antherozoids contained 

 in antheridia, which form small groups, called " sori," 

 visible to the naked eye, and scattered over the surface 

 of the frond. Padina pavonia has a fan-shaped frond, 

 encrusted with carbonate of lime ; it occurs on the 

 English coast with Dictyota dichotoma (Fig. 63). 

 Taonia and Halyseris ; but Dictyotacese otherwise 

 prefer warmer seas, and flourish especially well in the 

 tropics. Lobospira is exclusively an Australian genus. 



Fucaceae. — The large family of the Fucaceae is 

 characterized by their non-motile eggs and mobile an- 

 therozoids being contained in special conceptacula, 

 immersed either in the frond (Fucus, Fig. 65) or in 

 special fruit-bearing organs (Sargassum, Fig. 66). The 

 form of their fronds is widely different ; many of them 

 have air bladders in the continuation of the frond (Fucus 

 vesiculosus) or special air vesicles, allowing the plant to 

 float on the sea, when it has been torn away from its 

 support (Sargassum) . In the Arctic and northern tem- 

 perate regions Fucus, Pelvetia, Ascophyllum, Himan- 

 thalia (Fig. 68), Halidrys cover the coast with a dense 

 vegetation. In the southern region the Laminaria-like 

 Durvillea flourishes (Fig. 67). Australia and New 

 Zealand are very rich in Fucaceae ; we must also 

 mention the necklace-like Hormosira, with its parasite 

 Notheia (Fig. 69). Scytothalia also occurs in the 

 Antarctic. Turbinaria is strictly tropical ; Cystoseira, 

 Cystophyllum, and Sargassum (Fig. 64) belong to the 

 tropical and warm temperate seas. Of the latter genus 

 we must say a few words more, as it has a right to 

 claim the special attention of collectors. 



In each complete Sargassum we can distinguish two 

 parts — a short principal axis, with a tuft of rather 



