In plant cells its presence has been demonstrated in the Thallophytes and Bryophytes.
Cell Division.With the exception of a few plants among the Thallophytes, which consist of a single multinucleate cell, Caulerpa, Vaucheria, &c., the division of the nucleus is followed by the division of the cell either at once, in uninucleate cells, or after a certain number of nuclear divisions, in multinucleate cells.
In all plants, except Thallophytes, leaves are present at some period of their existence.
Have been described, but, as has been said, " by far the Algae greater number of the supposed fossil Algae have no claim to be regarded as authentic records of this class of Thallophytes " (Seward, 1898).
In the Thallophytes the cytoplasm may be segmented by constriction, due to the in-growth of a new cell wall from the old one, as in Spirogyra and Cladophora, or by the formation of cleavage furrows in which the new cell-wall is secreted, as occurs in the formation of the spores in many Algae and Fungi.