CHAPTER FOUR 



THE GENUS HALLASIA ROSEN VINGE 1924 



Among the incompletely known genera of the Zygnemataceae 

 is Hallasia, proposed by Rosenvinge in 1924 better to classify the 

 Zygnema reticulatiim described by Emma Hallas in 1895. The 

 young vegetative cells resemble those of Zygnema in having two 

 stellate chromatophores, but at the beginning of spore formation 

 there may be an increase in the number of chromatophores up to 

 seven. At the same time the cells may elongate, and as the cell 

 contents contract toward the enlarged middle portion the cell 

 cavity becomes filled with a cellulose-pectose colloid as in Zygne- 

 mopsis. The aplanospores also resemble those of Zygnemopsis in 

 being ellipsoid. When these aplanospores germinate, however, 

 there may emerge one, two, or three sporelings. This Rosenvinge 

 interprets as analogous to the germination of parthenospores in 

 Cosmarium from which two sporelings result. He has suggested 

 that the genus be placed among the Mesotaeniaceae or between 

 that family and the Zygnemataceae. 



The species has previously been classified in Zyg?iema Hallas 

 1895, in Debarya Transeau 1925, and in Zygnemopsis Transeau 



1934- 



Description of Species 



Hallasia reticulata Rosenvinge 1924. Rev. Algolog. 1, pp. 209-12. 

 Hallas. Bot. Tidsskrift. 20, pp. 1-16. 1895 (as Zygnema 

 reticulatiim^ . 



Vegetative cells 18-20 /x x 35-1 00 /j- with 2 to 7 stellate chromato- 

 phores in each cell; reproduction by aplanospores which are ellipsoid 

 and up to ^^5^'' in diameter, 60 /.i long; median spore wall yellow, scro- 

 biculate or irregularly reticulate; sporogenous cells lengthen up to 240 /a. 

 At germination the contents of the spores may become divided into 

 2 or 3 parts, from each of which a new filament develops. Sometimes 

 only a single plant develops from a spore. (Pi. X, Figs. 1-9.) 



Denmark, Copenhagen. 



According to Rosenvinge the plant has not been found again at the 

 site of the original collection. 



61 



