The characteristics of this species suggest that the peculiar Zygnema reticulatum, which was described by Hallas in 1895[B], is in reality a Debarya. The fact that the reproductive cells become filled with cellulose, that the aplanospores are very irregular in form and that the vegetative cells contain as high as seven chromatophores, are all in harmony with this idea. On this basis it is also easy to understand the most notable peculiarity of the species—that spores derived from cells with several chromatophores produce two or three sporelings.
With the addition of the two new American species and this Danish species Debarya reticulata (Hallas) nov. comb. the description of the genus needs to be modified as follows:
Vegetative cells cylindrical or constricted at the ends, varying from 1-16 diameters in length; chromatophore varying from an axile plate with two or more pyrenoids to stellate chromatophores, each with a central pyrenoid. Reproduction by zygospores formed of the complete contents of the gametangia; not cut off from the gametangia by partition walls; but in the process of conjugation, as the gametes pass into the conjugating tube, their place is taken by a secretion of cellulose. Aplanospores occupying only part of the sporogenous cell, the remainder being filled with cellulose. All spores variable in form. Parthenospores and akinetes occur not infrequently in some of the species. The walls of the aplanospores and parthenospores resemble the zygospores of the same species in their markings.
There are now eleven described species belonging to this genus. D. immersa W. West and D. africana G. S. West bear a close resemblance to Mongeotia sphaerocarpa Wolle. D. Hardyi G. S. West has much the same appearance as Mongeotia viridis (Kutz) Wittrock. D. desmidiodes W. & G. S. West, D. calospora (Palla) W. & G. S. West, D. reticulata, D. americana, and D. decussata have characters in common with the Zygnemas. D. glyptosperma has the vegetative characters common to several of the species, but its spores are quite unique among the Zygnemales.
ZYGNEMA Agardh.
Z. pectinatum (Vauch.) Agardh.
This is probably common in the eastern half of the United States at least. In Illinois along with the type occurs the variety conspicuum (Hass.) Kirchner, and a variety with large spores. This latter variety in fact is more common than the type.
var. crassum nov. var. Cellulis vegetativis 30-40µ × 20-80µ; zygosporis 40-55µ × 50-60µ, ceterum ut in typo.
Vegetative cells 30-40µ × 20-80µ; zygospores 40-55µ × 50-60µ, otherwise like the type. Type in herb. E. N. T. Collections No. 2350, 2392, 2660, 2685.