NOTES ON MELILOTUS ALBA 
423 
it has been generally accepted that in the Dicotyledons, plates 
are formed and divide the mother cells into tetrads. The re- 
cent work of Farr (2), however, shows rather conclusively that 
in certain Dicotyledons the divisions take place without the 
formation of cell plates and by constriction of the walls. 
The appearance of the giant grains which have partly di- 
vided renders it probable that Melilotus is one of the plants 
whose pollen mother cells divide by ingrowth of the walls. In 
the study of the sections a complete series of stages in the cut- 
ting off of one or more members of a tetrad can be found. 
Figures 26, 27, 28 and 30, Plate XIY, represent such a series. 
It is hard to conceive of a method by which a partial or com- 
plete formation of cell plates would give rise to the appearances 
found when all partly formed division walls arise very evidently 
through the ingrowth of ridges from the enclosing wall. 
The problems of the chromosome behavior in these abnormal 
grains and of the possible connection with hybridism remain yet 
open and as the structures are being found in other genera it is 
hoped that a comparative study may be undertaken. 
Department of Botany, 
State University of Iowa. 
LITERATURE CITED. 
1. Elving, F., Studien iiber die Pollenkorner der Angiospermen: 
Jenaische Zeitschrift Naturw., B. XIII, Jena, 1878. 
2. Farr, C. H., Cytokinesis in the Pollen-Mother Cells of Certain 
Dicotyledons: Memoirs of the New York Botanical Garden, 6, 253- 
317, 1916. 
3. Juel, H. 0., Beitrage zur Kentniss der Tetradenbildung: Jalir. 
Wiss. Bot., 35, 1900. 
4. Lyon, Florence May, A Study of the Sporangia and Gametopliytes 
of Selaginella apus and Sclaginella rupestris : Bot. Gaz., 31, 124-141, 
170-187, 1901. 
5. Nemec, B., Ueber den Pollen der petaloiden Antheren von Hya- 
cinthus orientalis : Bull. Int. Acad. Sci. Boheme, 1898. 
6. ShattucTc, Charles H., The' Origin of Heterospory in Marsilia: 
Bot. Gaz., 49, 19-40. 
7. Strasburger, E., Neue Untersuchunge uber den Befruchtungs- 
vorgang bie den Phanerogamen als Grundlage fur eine Tlieori der 
Zeugung, Jena, 1884. 
8. Wille, N., Uber die Entwickelungschichte der Pollenkorner der 
Angiospermen und das Wachstum der Membranen durch Intussuscep- 
tion, Christiana, 1886. 
