522 



A mm Is of the South African Museum. 



elliptical shape. This distinctive character of the chloroplast 

 strengthens the grounds for separating these species from TJlothrix, 

 but it also raises the question, whether an inclusion in the genus 

 Hormidium, which lias a chloroplast more like that of TJlothrix, is 

 advisable. It may be that a distinct genus should be established to 

 accommodate these species, but before arriving at a conclusion on this 

 point I prefer to await examination of material of H. fluitans. Atten- 

 tion may be drawn to the fact that special forms of chloroplasts are 

 not unknown in the Ulotrichales, a good instance being furnished by 



Fig. 14. — Hormidium rivulare, Kuetz. Resting-stages from sample 22. a, 

 b, and c represent progressively younger stages. All figures x 1000. 



the genus Mesogerron (F. Brand, Hedwigia, xxxviii, 1899, pp. 181-184), 

 which shows some remote points of resemblance to the species just 

 discussed. The genus Stichococcus is probably best restricted to those 

 species in which a filamentous tendency is little marked, the cells 

 being isolated and only, at times, forming short threads. 



In samples 22 and 38, and more rarely in 39, there occurred a fila- 

 mentous form, which I take to represent a resting-stage of 11. rim Ion 

 (Fig. 14), the more as ordinary filaments of this species were inter- 

 mingled with it and various transitional conditions could be found. 



The filaments (diam. 10 jx) have the appearance of having passed 

 thi-ough a resting-stage, involving the formation of akinetes, but un- 

 accompanied by any dissociation of the threads. In part the walls of 



