The cytology of zygospore-formation is not known in detail; the so-called gametes which fuse are multinucleate and are no doubt of the nature of gametangia.
In plants with multinucleate cells, such as Albugo, Peronospora and Vaucheria, it is usually a uninucleate cell differentiated by separation of the nuclei from a multinucleate cell, but in Albugo bliti it is multinucleate, and in Sphaero plea it may contain more than one nucleus.
Young tube (a) of the antheridium multinucleate oogonium (og) which introduces the male and antheridium (an).
The non-articulate tissue which occurs in Euphorbiaceae, Apocynaceae, Urticaceae, Asclepiadaceae, consists of long tubes, equivalent to single multinucleate cells, which ramify in all directions throughout the plant.
In multinucleate cells the division of the nucleus is independent of the division of the cell.
The contents of the antheridium are not set free, but that organ penetrates the oogonium by means of a narrow outgrowth, the fertilizing tube, and a male nucleus then passes over into the single oosphere, which at first multinucleate becomes uninucleate before fertilization.
In the group of the Siphoneae both these types of differentiation may exist in the single, long, branched, tube-like and multinucleate cell (coenocyte) which here forms the plant-body.