farr: cytokinesis of pollen-mother-cells 265 



in all parts of the division plane. In referring to the two types 

 of division characteristic of spore-mother-cells, Guignard (26c) 

 calls them "bipartition successive" and "quadripartition simul- 

 tanee." I shall refer to them as simply bipartition and quadri- 

 partition respectively. ^^ 



There is also some confusion as to the use of the word "tetrad. 

 Farmer and many zo61ogists have applied it to certain chromo- 

 somes in diakinesis, while it has also been used by others to refer 

 to the four spores resulting from a single mother cell. The latter 

 use, no doubt, grew out of the fact that these four spores are 

 frequently tetrahedrally arranged; and consequently there comes 

 the question as to whether four spores arranged in a monoplanal 

 rectangle or a rhomb should also be called a tetrad. In view of 

 this confusion and inasmuch as "the four spores" is generally 

 understood as referring to the product of a single mother-cell, 

 it seems more reasonable to restrict the term tetrad solely to the 

 chromosomes. 



One more instance of confused terminology might be noted in 

 this connection. The terms, "phragmoplast" and "cell-plate," 

 are used to refer to the same thing. The former is of more common 

 occurrence in the older literature, and its use has been resumed 

 recently by Ernst and Schmidt (15) and others. Inasmuch as 

 the structure in question is transitional, and during its existence 

 the cell is constantly undergoing transformation,, it would seem to 

 possess little similarity to such permanent cell-organs as the 

 plastids. Since the term, "phragmoplast," suggests such a rela- 

 tionship, it should probably be abandoned, and the term "cell- 

 plate" alone be retained. 



g. Quadripartition in cryptogams 

 As noted above, the phenomenon of quadripartition occurs in the 

 algae in the germination of the zygospore of Crater ospermum [Mou- 

 geotia] and in the formation of the tetraspores of Chylocladia and 

 other red algae. Quadripartition has been reported in a numbei: of 

 instances for the bryophytes. Strasburger was the first to do 

 this (67a), when in Pellia he reported a tetrahedral lobing of the 

 mother-cell, and division by cell-plates following. In the same 

 form Farmer has reported both bipartition (16c) and quadri- 

 partition {I6d) by cell-plates with the nuclei tetrahedrally ar- 



