SIPHONED. 59 



Family 3. Siphoneae. 



The thallus has apical growth, and in the vegetative condition 

 consists generally of one single (in the Valoniacese most frequently 

 of more) multinuclear cell, which may be much branched, and 

 whose separate parts in the higher forms (e.g. Bryopsi*, Fig. 57 ; 

 Caulerpa, Fig. 59, etc.) may be differentiated to perform the 

 various physiological functions (as root, stem and leaf). Vegeta- 

 tive multiplication by detached portions of the thallus (gemmae) ; 

 asexual reproduction by zoospores, akinetes, or aplanospores. 

 Sexual reproduction by gamete-conjugation, rarely by oogamous 

 fertilisation. The zygote or oospore germinates as a rule without 

 any resting-stage. 



Most of the Siphonene occur in salt water or on damp soil. 



FIG. 56. Botrydium granulatum : a an entire plant forming 1 swarmspores ; b swarm- 

 spores; c an individual with gametangia ; d, gamete; e,f,g conjugation; h zygote 

 seen from above ; i the same in a lateral view. 



Many (e.g. Dasycladact'W) are very much incrusted with lime, and 

 occur, in the fossilized condition, in the deposits from the Cretaceous 

 period to the present time. The Siphonete are connected by their 

 lowest forms (Botrydiacew or Valonia) with the Protococcacea?, but 

 show also, through the Valoniacese, points of relationship to the 

 Cladophoracece. 



Order 1. Botrydiaceae. The thallus in the vegetative condi- 

 tion is unicellular, club-shaped, with a small single (Codiolwrn) or 

 repeatedly dichotomously branched system of colourless rhizoids 

 (Botrydium, Fig. 56 a), by which it is attached to objects immersed 

 in salt water (Codtolum) or to damp clay soil (-Botrydium). 

 Asexual reproduction by zoospores with one (Botrydium) or two 



