348 Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



This plant was found with tetraspores, antheridia and cysto- 

 carps in the month of March, 



It was dredged in deep water about 30 — 40 meters and in a place 



where strong currents prevail. 



St. Jan: In the sound between this island and St. Thomas: off 

 Cruz Bay. 



Geogr. Distrib.: Florida. 



Subfam. 3. Nitophylleæ. 

 Martensia Hering. 



1. Martensia Pavonia J. Ag. 



J. Agardh, Spec. Alg., vol. II, p. Ill, p. 831. Kützing, F., Tabula^ 

 Phycol., vol. XIX, tab. 60, figs, e — n. Svedelius, N., Über den Bau und 

 die Entwicklung der Florideengattung Martensia (K. Sv. Vetenskapsakad. 

 Handl., Band 43, No. 7, Uppsala 1908). 



Mesotrema Pavonia J. Ag., Nya algformer in Öfvers. k. Vetensk.- 

 Akad. Forhandl., 1854, p. 110. 



Svedelius in his very valuable work on the genus Martensia 

 gives an exhaustive description of the present species based partly 

 upon material collected by me at the island of St. Croix. 



Having now examined some more collections of mine of this plant 

 I am able to add a few remarks to Svedelius' description. 



Martensia Pavonia grows epiphythic upon other algæ between 

 whose filaments it becomes entangled, furthermore fixing itself 

 by means of rhizoids which seem to be able to grow out nearly 

 everywhere from the margin of the thallus (Fig. 344). The rhizoids 

 issue not only from the coherent tissue, but also from the reticular 

 part of the thallus (cp. the figures of Svedelius, 1. c, p. 34, fig. 34). 

 A supposition expressed by Svedelius and one to which I am quite 

 willing to subscribe is that parts of the plant torn loose or such ones 

 becoming free by the decomposition or dying away of the net 

 are able just by means of these rhizoids to fix themselves and give 

 rise to new plants. 



Martensia Pavonia (Fig. 345) together with the Australian 

 Martensia denticulata form a small, distinguished group within the 

 genus Martensia, both species being by J. Agardh referred to his 

 subgenus Mesotrema. What especially characterizes this group is 

 the belts of coherent tissue and reticular tissue successively following 



