CHLOROPHYCE^ 121 



as most probably nearer the lower limits of 

 archegoniate plants than are any other Algae. 



The other Chloropliycece exhibit isogamous repro- 

 duction viz., the conjugation of equal gametes 

 provided with cilia ; and in the case of the Con- 

 jugatse, which are confined to fresh-water, the con- 

 jugation of non-motile gametes. 



Non-sexual reproduction by zoospores and un- 

 ciliated spores also occurs freely and abundantly in 

 the Chlorophycece. 



' The Caulerpacece, Vaucheriacece, Codiacece. Udo- 

 teacece, Dasydadacece, and Valmiacecc which form a 

 group together (usually called Siphonccc) are dis- 

 tinguished from all other Algae by the fact that 

 their often complicated thallus consists in reality of 

 a single cell with many nuclei. In Valonia this one 

 cell retains a primitive, more or less globular, shape, 

 but in the other orders it is much branched and the 

 branches gain coherence from being interwoven, laced 

 together by haptera, incrustation, etc. In Ccmlerpa 

 alone the lumen of the great cell is strengthened 

 internally by numerous trabeculse or crossbeams 

 that run from wall to wall. 



CAULERPACEJU. 



General Characters. The order is represented by 

 the single genus Caulcrpa (though systematists have 

 proposed to split it up into several genera on wholly 

 insufficient grounds) containing about eighty much 

 varied species. They are exclusively marine. In some 



