82 Dr. F. Cohn on the Development and Propagation 



Spharoplea annulina, Ag., is one of the rarer freshwater Algae, 

 which is not observed, Uke most of these plants, everywhere and 

 at all seasons, but only at long intervals and under peculiar cir- 

 cumstances ; it consists, like all the Confervse, of cells of variable 

 length, connected in a single row into long filaments, and is 

 characterized by a peculiar arrangement of the chlorophyll. 

 Ehrenberg has already remarked that it covers extensive surfaces 

 about Berlin with a red coating, and hence may have given rise 

 to traditions of " blood-rain/' Near Bremen, where it was dis- 

 covered by Treviranus, it occurs upon flooded tracts. At Breslau 

 I found it the first time at the end of October, last year, in 

 a potato-field which had been laid under water by the great 

 overflow of the Oder in the last week of August. The Sphaeroplea 

 covered the field, which had dried again after the retreat of the 

 water, as an almost uninterrupted felt, of a beautiful red-lead or 

 vermilion colour on the smooth upper surface, and green on the 

 under side, where it was disentangled into the separated filaments. 

 The red colour depended upon the spores with which the fila- 

 ments of the Sph(Broplea were completely filled up ; only those 

 filaments which were exposed to light and air on the surface of 

 the felt fructified ; the under side, resting on the ground, con- 

 tained only vegetative filaments of the normal green colour. 



The structure of the Spharoplea-sipoves is very simple ; they 

 are red globules, usually from 1-125 to 1-100'" in diameter, 

 surrounded by two hyaline membranes, of which the inner lies 

 close upon the contents, while the outer is somewhat separated 

 and is elegantly creased. The spores of Sphceroplea are usually 

 described as stellate; Kiitzing however states that they are 

 encircled by spiral bands. Both these assertions are justified to 

 a certain extent : it depends upon the position of the spores 

 whether they look like many-rayed stars, or as longitudinally 

 streaked, smooth-bordered globes. The outer coat of the spore 

 is so folded that the folds meet at the two poles of the globe like 

 so many meridians. Hence if we look at the pole of a spore, 

 the folds are seen surrounding the globe like a frill, in a sharp- 

 angled zigzag ; while if we look upon the equator of the spore 

 with the axis parallel to the object-glass, the folds may be traced 

 in their whole course as longitudinal lines. In many spores, 

 especially the large ones, the plaiting of the outer coat is very 

 irregular, and forms merely wart-like elevations without any 

 definite arrangement. Sulphuric acid causes an expansion of 

 this coat, but does not destroy it ; iodine and sulphuric acid colour 

 it bright yellow. 



The contents of the spores consist of rather large starch-gra- 

 nules, and protoplasm which is coloured bright vermilion-red by 

 a peculiar colouring matter ; they contain a red oil which stands 



