Ecology of Zygnema stellinum Vauch. during desiccation of a shallow body of water.

the effect of desiccation on the green alga Zygnema, a typical aquatic form of the order Conjugatae, family Zygnemaceae, is investigated. The vegetative reproduction of Zygnema occurs with the separation of the filaments in two different ways. It is shown that changes take place in cell morphology during desiccation. After division most of the cells acquire the shape of a square. These are usually half as large as the vegetative cells prior to division. Also, the form and color of the chromatophores change; they become green-brown, i.e., Zygnema falls into a state of rest, since no cell division is observed. During this state of rest the filaments suffer the unfavorable conditions of summer drought. In the fall, at the end of August, with the shortening of the day and reduction of temperature, the alga develops parthenospores for overwintering.