K. BORGESEN 



r\ r '\ Island is most like the form called 



Acrocarpus pusillus by KUTZING in 

 his »Tabulse», vol. 18, pi. 37, and not 

 Acrocarpus pulvinatus. The Easter 

 Island specimen grew on a small shell 

 and was two — three mm high. The 

 creeping rhizome-like partofthethallus 

 was terete and about 1 1 ;j. thick. Is was 

 firmly attached to the substratum by 

 means of vigorous rhizoids deeply sunk 

 into the shell. Opposite the rhizoids, 

 from the upper side of the rhizome, erect 

 leaf-like shoots grow out, at first single, 

 later often more or less cespitose. 



Tetrasporangia are formed in the 

 tips of the leaf-like branches. 

 The Easter Island plant certainly comes very near var. conchicola Piccone 



and Grunow, Algol. Eritrea (N. Giorn. Bot. Ital., vol. 16, 1884, p. 316); comp. 



OKAMURA, List of Mar. Algae collected in the Caroline and Marianne Islands 



(Bot. Mag., vol. 30, 1916, p. 9, fig. 6). It also resembles var. minusatla Weber 



van Bosse, Alg. Siboga, p. 226. 



Area of distribution: Atlantic and Mediterranean coast of Europe, Maroc, 



Japan, Australia, Easter Island. 



Fig. 26. Gelidium pusillum (Stackh.)LeJol. Part 

 of a plant; most of the rhizoids are broken, c. 12 /i. 



Caulacanthus Kiitz. 



C. spinellus (Hook. f. et Harv.) Kiitz. — Figs. 27, 28. 



Kutzing, Species Alg., p. 753. — Rhodomelal spinella Hook. f. et Harv.; 

 Hooker, J. D. and W. H. Harvey, Algae Novae Zelandiae (The London Journal 

 of Botany, vol. IV, 1845, p. 534). 



A few sterile fragments of an irregularly ramified filamentous alga belong 

 I think to this species. The branches, arranged without any order at all are 

 sometimes short, spine-like, sometimes prolonged. 



The thallus grows by means of an oblique top cell from which a tissue 

 is formed consisting of a central row of cylindrical cells, encircled by some 

 smaller ones which again gradually pass into a cortical layer of small cells. 

 On a longitudinal section the cells of the central tube measure about 25— 40 jj. 

 across and 100— 150 [x in length, according to the strength of the axis. These 

 large cells contain bundles of raphides. The cells next to these are also rather 

 long about twice their own width; the following are shorter and shorter, as we 

 proceed toward the surface. 



The thallus is from 150 u. — 200 [i. thick. It is fixed to the substratum by 

 means of small discs growing out everywhere from the surface of the thallus 

 and composed of a bundle of rhizoids. By means of such discs also branches 

 of the same individual get united. In this respect it quite agrees with Wurde- 



