61 



gularly polygonal plate-shaped chromatophores, forming by 

 means of their prolonged corners a rather dense network in the 

 young parts of the thallus (Fig. 41 k), in the older the chromato- 

 phores are of a more elongated form and more openly placed. 

 In the middle of the chromatophore a pyrenoid is present. Below 

 the chromatophores the numerous nuclei occur distributed rather 

 regularly. 



This species has been gathered in shallow water 2 — 3 feet, 

 and here in a rather exposed locality, and in deep water, down 

 to about 50 meters. 



It is found: St. Croix, at White Bay on tlie soutli side of tlie island 

 and St. Jan in the sea round this island: off Cruz Bay, Marys Bluff, Rams- 

 head, Annaberg etc. 



Geogr. Distrib. West Indies, South America, Indian Ocean. 



SiphonocladuS (Schmitz) Borgs. 



Siphouocladus tropicus (Crouan) J. Ag. 



J. Agardh, Till Algernes Systematik, 5te afd., p. 105. (Lund Univ. 

 Arsskr. 23, 1887). Borgesen, F., Contributions a la connaissance du genre 

 SiphonocladuS Schmitz (Overs, k. danske Vidensk. Selsk. Forhandl., 1905, 

 p. 259). Howe, Phycological Studies, I. (Bull. Torr. Bot. Club. 32, 1905, 

 p. 241). 



Apjohnia tropica Crouan in Maze et Schramm., Alg. Guadel. p. 105. 



SiphonocladuS tropicus grows in tufts epiphytic upon other 

 algse or is found loose lying as /Egagropila-\ike clumps ; it is often 

 cast ashore in rather large quantities. I have not succeeded in 

 finding it growing on rocks but most probably it also does so. 



Referring for more detail to my above-quoted paper I shall 

 here give a short survey of the development of the thallus. 



As is the case in so many related forms so also here the thal- 

 lus at first consists of a single large cylindric-claviform cell fastened 

 to the substratum by means of irregularly ramified rhizoids 

 (Fig. 44 a). In the older plants these rhizoids get very thick 

 walls (Fig. 45). In my earlier paper I mention that I have not 

 succeeded in finding cross walls in the rhizoids ; having now 

 during my last visit to the islands gathered a rich material also 

 of epiphytic specimens fixed to other algse I have been able to 

 examine the basal part of the plant in more detail and have found 

 that cross walls occur often in the rhizoids (Fig. 45). Likewise 

 I have seen that young erect shoots can grow out from the rhi- 

 zoids (Fig. 46). In these much starch is present. 



