102 



gradually a little smaller towards the node where the cells are relatively very small and thick- 

 walled. In the growing apex the node is already visible as a mass of small cells (PI. XV, fig. 1 1). 



From the node, which increases in thickness with the thickness of the frond, spring 

 forth the branches and in one species of this genus M. stelligerum the node, the cells of 

 which struck me as not being particularly small, increases also in length. This takes place 

 thnui'di the cells of the central strand of the calcified joint losing their chalk where they are 

 in contact with the node. At the periphery of the central strand cell division takes place 

 which causes the still calcified cortical layer to be thrown off, either partially or in old plants 

 almost entirely. 



By this process the articulated appearance of the young plant disappears gradually and 

 a loncr pliable horny branch is seen with remnants of the calcified cortical layer adhering to it 

 here and there. Such forms of M. stelligerum were described by Lamouroux as Amphiroa 

 jubata and A. interrupta. Sectioning the horny node of such plants I was struck by the total 

 disappearance of what everybody is used to consider as the typical structure of the Mclobesiaceae. 

 The cells <>f the central strand were no longer standing in straight rows one above another as 

 they had done in the young plants. They now had thick walls, had been pulled in various 

 directions and the places where their protoplasts clung together, had grown out, giving very 

 different shapes to the cells, which looked in fact like any ordinary small-celled alga-tissue, 

 such as one meets in so many Florideac. The cortical layer consisted of rather large cells, 

 horizontally stretched and growing smaller towards the periphery. 



I have dwelt at some length on this structure of old plants of M. stelligerum because 

 it explains the structure of my new genus Litharthron. M. stelligerum is the link between 

 M. charoides and Litharthron australis, but it bas more characters in common with M. 

 charoides. Young plants in fact of M. stelligerum have the same anatomical structure as M. 

 charoides ■. it is only with increasing age that such characters appear which we shall find 

 again, only still further developed, in Litharthron australis. 



The three species of the genus Metagoniolithon are: 

 i . M. charoides. 



Amphiroa charoides Lamouroux, Hist. d. Pol. flexibles, iSiö, p. 301. 



Sturdy plants with branching fronds, distinctly articulate. Joints often a little flattened 

 from 1 to 3 cm. long and up to 2 mm. broad. Nodes rather short, entirely surrounded by pseudo- 

 whorls of branches, no true whorls, for the branches do not appear simultaneously. Anatomical 

 structure of joint consists of many layers of cells all of the same dimension, the cells of each 

 horizontal row communicating by thin places in the longitudinal wall. In the node the cells 

 are very small and have thick walls. Fructification consists of conceptacula, which appear first 

 on the inner side of the branches but may afterwards cover the whole branch. 



5 plant is found in South Australia; the specimens which I received under the name of 

 mphiroa charoides from the West Indies belonged to Amphiroa foliacea. I therefore do not 

 know, whether specimens of M. charoides have indeed been found in that region. 



