252 



Siphonodadiales 



segment from which they were derived (fig. 162 A). Successive formation of 

 branch-segments sometimes results in a thallus with dichotomous or verticillate 

 branches, although as a rule the branching is irregular. The main coenocyte 

 is attached to its substratum by numerous well-developed rhizoids or haptera 

 (fig. 162 G), which grow out from the small lentiform segments that occur 

 in great numbers at the basal end of the adult plant. 



Fig. 162. Valonia utricularis (Both.) Ag. A, complete plant showing a ' stem-cell ' with five 

 'branch-cells' grown out from the apex and two 'rim-cells' (a, a) which have not yet grown 

 out into ' branch-cells ' ; near the base of the ' stem-cell ' are numerous smaller ' rim-cells ' 

 and three at the extreme base have grown into rivet-shaped rhizoids, x 4. B, single 

 cosnocyte developing zoogonidia. C, older rhizoids. D, zoogonidia. E and F, developing 

 zoogonidia. (A, after Schmitz ; B E, after Famintzin, from Wille.) 



In Dictyosphseria the contents of the very young coenocyte, which may be 

 ovoid, cylindrical or irregular, are divided by segregative cell-division, first 

 into several coenocytes, and afterwards by successive segregative divisions 

 into numerous segments which are so compact as to be angular by compres- 

 sion. Numerous small lenticular cells (they have each only one nucleus) are 

 formed in the peripheral parts of the segments. Some of those near the base 

 develop into haptera for attaching the Alga to the substratum, but others, 



