272 GEACE A. DUNN 



give rise to a mother cell. This results in the formation of an 

 enormous number of tetrasporangia. The average number of 

 tetrasporangia in a piece of the thallus 1 cm. long is 25,000. 



At an early age the subcortical cell destined to develop a 

 mother cell of a tetrasporangium, can be distinguished from the 

 adjoining vegetative cells of the same rank by its greater size 

 and a difference in staining properties (fig. 1, C). The chromato- 

 phore of the mother cell of the tetrasporangium is a clathrate, 

 hollow ellipsoid (fig. 1, C, D). As the mother cell matures, 

 the portions of this ellipsoid become elongated into iixegular, 

 narrow bands (fig. 1, E). A few linin fibrillae radiate out from 

 the nucleolus to the nuclear membrane. All the chromatin is 

 in the nucleolus, which is never homogeneous and sometimes 

 contains as many as three vacuoles (fig. 1, F, G). The mother 

 cell of the tetrasporangium up to a fairly late stsge in its de- 

 velopment remains connected to the cortical cells at its outer 

 end (fig. 1, D). None of the mature tetrasporangia show these 

 connections. 



C. THE MATURE ONE-CELLED TETRASPORANGIUM 



The cell conteyits. The mature tetrasporangium is 66^ in 

 length and 44iu in width. It is highly vacuolated. The chro- 

 matophore and most of the cytoplasm are peiipheral. The 

 ribbon-like strips of the chromatcphore have, at regular inter- 

 vals, gradually narrowed and become thread-like. The chro- 

 matophore then appears to consist of small irregular plates 

 about 1.4/x in diameter which aie airanged in rows and are 

 connected by narrow cytoplasmic thieads (fig. 1, H). The 

 diameter of the nucleus is 8.4^ and that of the nucleolus is 3.1ju. 

 The number of linin fibrillae is gieater than that in the nucleus 

 of the mother cell of the tetrasporangium (fig. 1, F, I). All 

 the chromatin is in the nucleolus. 



The distribution of the chiomatin in the tetrasporangium 

 nucleus of Dumontia differs, as far as known, ficm that of all 

 other Floiide^e. In the tetraspoiangium nucleus of Griffithsia,- 



* Lewis, L F. The Life History of Grijfilhna Bornetiaaa. Annals of Botany 

 23: 030-690. 1909. 



