224 Siphonales 



conjugate form parbhenospores which soon grow into new plants. It would 

 seem that the motile cells are probably of the nature of zoogonidia which are 

 also facultative gametes. 



Wille has placed Protosiphon alongside Botrydium in the ' Hydrogastracese ' ; and 

 Oltmanns includes Blastophysa along with it in the Protosiphonaceee, which he places as 

 a family of the Protococcales. There is only one known species, Protosipkon botryoides 

 (Kiitz.) Klebs. 



It seems natural to include the genus Halicystis (Areschoug, 1850) in 

 the family Protosiphonacere. It is a small genus of marine Algas in which 

 the thallus consists of a single round or ovoid, bladder-like coenocyte, about 

 the colour and size of a green grape, having a short basal stalk terminating 

 in a minute disc by which the plant is attached to its substratum. The 

 substratum consists of shells or stones, or sometimes the disc bores its way 

 into the calcined crusts of Lithothanmion (Kuckuck, '07). No rhizoids are 

 formed. There is but one cavity, that of the bladder-like vesicle passing 

 downwards into the cylindrical stalk. The wall is very finely stratified, and 

 lining its interior there is a delicate layer of protoplasm containing numerous 

 small nuclei and chloroplasts. The greater part of the volume of the lumen 

 is filled with cell-sap. The chloroplasts are rounded or oval discs, wholly 

 destitute of pyrenoids but containing starch. The nuclei are also flattened 

 discs, scattered irregularly or sometimes in pairs through the entire lining 

 layer of protoplasm (Murray, '93). 



Zoogonidia are formed in the upper part of the coenocyte, the protoplasm 

 of the lower part remaining sterile, although there is no separating wall 

 formed between the two portions. Both macro- and microzoogonidia have 

 been observed by Kuckuck ('07). They are biciliatcd and escape through 

 one or more apertures in the old wall. The microzoogonidia may perhaps 

 also function as isogametes. 



Halicystis has usually been placed alongside Valonia in the Valoniaceas, 

 but Schmitz, and also Murray, have given cogent reasons for its inclusion in 

 the Siphonales. Although Halicystis bears a striking resemblance to 

 certain species of Valonia, it differs in the more irregular disposition of the 

 nuclei, in the rounded chloroplasts without pyrenoids, in the absence of 

 rhizoids, in the feeble stratification of the wall, and in the fact that it never 

 becomes at any time more than a single coenocyte. H. ovalis (Ag.) Aresch. 

 extends from subtropical regions into the N. Atlantic and North Sea. 

 H. parvala Schmitz is confined to the Mediterranean. 



Family ChsetosiphonaceaB. 



This family includes only the genus Ch&tosiphon Huber ('93) of which there is but one 

 known species, Ch. moniliformis, an alga occurring as an endophyte in the dead and 

 discoloured leaves of Zostera marina. The thallus consists of a richly branched coenocyte, 

 rather deeply constricted at frequent intervals, but without transverse walls except in 



