18 Dansk Botanisk Arkiv, Bd. 2. Nr. 2. 



This species belongs to the littoral and the upper sublittoral 

 region. 



It occurs upon rocks and stones and is found even in the 

 most exposed places where the waves constantly splash the rocks. 



St. Croix: Cane Bay, Northside ; St. Thomas: Store Nordside Bugt, 

 near the entrance of the harbour. 



Geogr. Distrib. Mexico, West Indies. 



7. Ectocarpus elachistæformis Heydr. 



Heydrich, F., Beitäge zur Kenntnis der Algenflora von Kaiser-Wil- 

 helms-Land (Deutsch Neu Guinea). Berichte der deutsch, bot. Ges., Bd. X, 

 1892, p. 470, pl. XXV, flg. 14. 



Jn the cryptostomata of an old Sargassum vulgare which was 

 quite overgrown by various algæ, e. g. Chantransia, Erythrotrichia, 

 Rivularia etc. was found a small Ectocarpus which filled up nearly 

 the entire cavity. 



This plant I think can be referred to Ectocarpus elachistæ- 

 formis Heydr. even if it shows some differences. 



It reached a height of about 1 — 3 mm and had horizontal, 

 irregularly bent, basal filaments growing more or less together 

 forming in this way a small irregular disc (Fig. 11 a). From this, 

 short rhizoids, consisting only of a few cells, penetrate downwards 

 into the tissue of the host plant (Fig. 11 b, c) ; and upwards long 

 assimilating filaments and plurilocular sporangia are produced. 



The assimilating filaments are thickest at their base, here 

 about 10 — 14 (j broad, upwards thinner, about 8 p. ; they consist 

 of cylindrical cells which below are only a little longer than 

 broad, the growing point being here ; higher up the cells grow 

 longer reaching a length of up to 5 times their own width. The 

 assimilating filaments are simple throughout with the exception 

 of a few quite short branches near their base upon which terminal 

 plurilocular sporangia are placed. 



These short branches consist most often of only a single 

 cell sometimes of a few. Such short branches with plurilocular 

 sporangia are also found growing immediately out from the cells 

 in the basal filaments. 



Now and then also sessile sporangia placed immediately 

 upon the filaments occur. 



The plurilocular sporangia are elongated lanceolate, broadest 

 a little below their middle. They are about 100 — 140 p long 

 and 16 — 23 p broad. The zoospores escape by means of a hole 

 in their top (Fig. 11 b). 



