25! 



F. liORGESEK 



The plant was attached to Nitophyllum spec. From the decumbent short 

 filament, the long erect one arises. At the base the filament was 12 \>. thick, 

 somewhat higher up 19 ;j., a 1 i tie above the sporangium 24 ;j.. Along the 

 intercalary growth-zone the width is about 23 ;j.; from here the filament evenly 

 tapers into a pseudo-hair like prolongation with cells about 15 ;j. thick and 

 So [j. long. 



The plurilocular sporangium is ovate fusiform, 80 |j. long and 24 [j. broad. 

 It was placed upon the basal cell of a short branch. In the plant of Mme. 

 WEBER the sporangia are sometimes sessile, sometimes placed upon a short 

 pedicel. 



Fam. Ralfsiaceae. 

 Mesospora Weber van Bosse. 



M. Van-Bosseae nov. spec. 1 — Fig. 9. 



Thallus 2 — 3 cm et ultra altus e disco basali et filis erectis constructus. 

 Discus basalis e filis repentibus coherentibus subdichotomo divisis compositus 

 unde fila erecta oriuntur. Fila erecta in parte basali e cellulis latioribus quam 

 altis et plus minus cohaerentibus stratum subparenchymaticum formantibus, in 

 parte superiori libera, subclavata e cellulis cylindricis ca. 24 |j. longis et 8 — 11 ;j. 

 latis, ad apicem versus cellulis gradatim latioribus ad 16 \s. latas composita. 



Sporangia plurilocularia in superiori parte filorum formata. 



Through the great kindness of Mme. Weber I have been able to compare 

 my plant with original material from the Siboga Expedition. 



By means of this and the detailed description of Mme. Weber I have 

 convinced myself that the plant from Easter Island, even if it agrees with 

 the Malayan one in many respects, nevertheless differs essentially in others, 

 making it necessary to regard it as a new species. 



The plant grows on stones to which it adheres firmly with its wholeiower 

 surface. It forms dark brown or nearly black crusts as much as 2 — 3 cm in 

 diameter or even more. 



The basal part of our plant is formed of several brown layers of old 

 decayed tissue, often including blue green algae, in transverse section presenting 

 a picture very like that found in fig. 43 of Mme. Weber. 



I have succeeded in finding a small marginal portion, represented in 

 fig. 9 b. It is composed of creeping, congenital filaments growing in length by- 

 means of a top cell. By transverse walls these filaments are divided into more 

 or less isodiametric cells. The filaments are about 10—15 u thick, the top-cell 

 often 20 {i or more. The filaments are radiant to all sides and by and by, as 

 the disc expands and the width of the outermost ends of the filaments increases 

 the cells show longitudinal walls, the filaments thus becoming dichotomously 

 divided. 



At a very early stage erect filaments arise from every cell of the basal 

 stratum. These erect filament grow vertically, standing quite close together. 



1 I have the great pleasure to name this species in honour of Mine. Dr. A. Weber van 

 Bosse, the indefatigable explorer of the algal flora of the. Malayan Archipelago. 



