Notes on the Zygnemales

Abstract

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 0. Borge and 0. 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