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When one studies a young growing branch of Amphiroa in a decalcified state and in 

 longitudinal sections, the nodes are indicated by the different colour of the membrane. That is 

 all. The whole young top presents the same disposition of cells throughout its whole length 

 and the rows of long and short cells succeed one another quite regularly. 



On the other hand if one studies longitudinal sections of either Arthrocardia, CJieilo- 

 sporum, Jania^ Coralliua, Lithothrix or of our new genera Metagoniolithon and Litharihron, 

 the disposition of the cells at the top of the young branch is quite different in the region of the 

 future node, corresponding with the structure of the adult node in each of these latter genera. 



It appeared to me that this difference in anatomical structure was indeed a good character 

 whereby to distinguish the genus Amphiroa. It seemed to me to be of great value since the 

 study of the development of the cystocarp offers many difficulties, arising from the smallness 

 of the object; and even if one succeedecl in tracing its development, it is highly probable that 

 it would follow the same mode as Solms-Laubach has described for the Corallinae and thus 

 not afford a good character whereby to distinguish Amphiroa either from Arthrocardia or 

 Chcilosporum. How difficult such research would be is shown clearly by the very few conceptacula 

 with procarpia I met with during my whole investigation. In my preparations I saw mostly 

 conceptacula with ripe or unripe tetraspores; next came antheridia and conceptacula full of ripe 

 carpospores. Rarely have I seen a conceptaculum with procarpia or cystocarp-spores in course 

 of development. 



Since however the anatomical structure of the frond first recognized by Zanardini and 

 of the node proved indeed a good generic character whereby to distinguish the genus Amphiroa, 

 I have had to strike out of that genus a great many species that had been described - - often 

 not by their authors, but by succeeding ones — as belonging to this genus. The algae which 

 Lamoüroux first mentioned as belonging to Amphiroa, have the same structure as mentioned 

 by Zanardini. They constitute the types of the genus; and other species, differing from these 

 types even though they were also called Amphiroa by Lamoüroux in his later work of 1816, 

 must be taken out of the genus. 



The genus Amphiroa when cleared of all species that are only like it in outward 

 appearance is a very well limited group. The presence of nodes distinguishes it from Litho- 

 thamnioneae \ the continuity of the frond - - the same anatomical structure of the central strand 

 throughout the whole frond — , distinguishes it from Arthrocardia, Chcilosporum or Corallina, 

 where long cells are intercalated between two succeeding joints. Solms-Laubach has already 

 called attention to the fact, that Amphiroa has very many afhnities with Lithothamnioii; and 

 the results I obtained during my investigations tend only to show the near relationship of 

 Amphiroa to LithotJiamnion. The anatomical structure of Amphiroa, as it shows itself in distinct 

 periods of growth, is a character which we find also in LitJiotliamnion, and it is interesting to 

 observe how the node is gradually developed in species of Amphiroa with broad, often irregularly 

 branched fronds as A. crassa or A. tribulus, the fronds of which resemble outwardly small 

 forms of LithotJiamnion. We see in these two species, as will be shown more fully in the following 

 pages, that the cells of the central strand alone contain no chalk and form a node often entirely 

 surrounded by a layer of calcified cells. A further stage in the development of the node is 



