CHLOROPHYCE.E 165 



are produced in Siphonocladus as a result of injury of 

 the thallus. 



The Geographical Distribution. The distribution 

 of the order is mainly tropical only the genera placed 

 here with hesitation Halicystis and Blastophysa 

 reaching the North Atlantic and North Sea. 

 Valonia, with about fifteen species, is of wide occur- 

 rence in the warmer seas ; Apjohnia, with two species, 

 is found in Australia and at the Cape ; Siphonocladus, 

 with several species, in the Mediterranean and in 

 tropical seas ; Chamccdoris (one species) in all tropical 

 seas ; Dictyosphceria (two species) in the West Indies 

 and Australia ; Struvca (six species) in the tropics for 

 the most part ; Boodlca (one species) in the Pacific ; 

 while Microdictyon and Anadyomene, with six or seven 

 species each, are also mainly tropical. 



CLADOPHORACE.E. 



General Characters. The thallus is always a row 

 of single cells in some cases branched, in others 

 simple, and since these cells contain each several 

 nuclei, it is very difficult to say where the dividing 

 line is to be drawn between Cladophoracece and 

 Valoniacew between the old order Siphonecv and 

 the other Chlorophycece. In the typical Cladophor- 

 accw the filaments, whether branched or simple, grow 

 erect in tufts, but in Gomontia the habit of the whole 

 plant is modified by its living within the substance of 

 shells which the filaments perforate. Reproduction is 

 effected by the conjugation of equal gametes, and by 



