NOTES ON THE ZYGNEMALES.[A]
Edgar Nelson Transeau.
The following notes principally concerning North American Zygnemales are based on a study of the specimens accumulated in the course of eight years collecting in central Illinois; a collection made by Mr. Charles Bullard, of Cambridge, Mass., in Massachusetts and New Hampshire; the specimens distributed in the Phycotheca Boreali-Americana by Collins, Holden and Setchell; the specimens distributed in American Algae, by Miss Josephine E. Tilden; the specimens in the U. S. National Herbarium; and small collections sent me by Professor Farlow, Miss Tilden, Professor A. B. Klugh, Professor D. S. Johnson and Miss Grace Stone. They have been compared with the species distributed by Wittrock and Nordstedt in their “Algae Aquae dulcis exsiccatae,” and other valuable European and South American specimens sent me by Professors O. Borge and O. Nordstedt.
In determining almost any species of the Zygnemales it is absolutely essential that the specimens show both the vegetative cells and the mature spores. With the exception of a few species of Mougeotia the spores are colored either yellow, brown, or blue when they are mature. The characteristic markings of the median spore wall do not develop usually until this color appears. Consequently it is useless to attach names to vegetative specimens based on dimensions and number of chromatophores. Keys based on such characters are not only useless, but misleading.
Judging from my experience in Illinois it is highly probable that the list of North American forms will be considerably augmented, when intensive studies have been made at localities in the Southern United States. The most satisfactory method of collecting these forms is to take samples from the various ponds and streams at regular intervals of ten days, or two weeks, throughout the growing season. Many of the species show local variations and considerable experience is needed before many of the forms can be satisfactorily classified. The writer has in course of preparation an illustrated key to the group, in which figures for all of the species will be published.
DEBARYA Wittrock.
This genus is in many respects the most generalized of all the Zygnemales. It is distinguished by three important characteristics: (1) the entire contents of the gametangia enter into the making of the zygospore; (2) the zygospore is formed in the conjugating tube and is not cut off from the other parts of the gametangia by partition walls; (3) as the gametes move toward the tube during conjugation, their place is taken by a secretion of cellulose, which renders the gametangia solid and highly refractive. This secretion also occurs when a vegetative cell forms an aplanospore.
Debarya glyptosperma Wittrock.
This species has been recorded for America. It is not uncommon in Massachusetts and has also been found in Minnesota and Florida. In P. B.-A. No. 808 from Boswell, California is a somewhat smaller variety with blue spores associated with Zygnema peliosporum Wittr. The spores are common in the material and the vegetative cells and filaments occasional. Following is a diagnosis for this variety:
Var. formosa nov. var. Cellulis vegetativis 7.5-9µ latis; zygosporis 24-30µ × 30-42µ, caeruleis; ceterum ut in typo.