470 THE AMERICAN NATURALIST. (VoL. XXXIX. 
somes in sporophyte and gametophyte for more than fifty forms. 
This list may be found in Coulter and Chamberlain's recent 
text-book, Te Morphology of the Angiosperms, 1903, p. 81. 
Farmer's accounts of the number of chromosomes in the Hepaticze 
have been confirmed and extended by myself (Davis, '99, : 01a) 
and by Moore (:03). The more recent literature, especially as 
it concerns the events of spindle formation in the mitoses char- 
acteristic of sporogenesis has been treated in our account of the 
spore mother-cell (Amer. Nat., vol. 38, p. 725, Oct., 1904). 
There are two chief periods in the processes of sporogenesis 
as illustrated in all groups above the thallophytes: (1) a growth 
period and (2) a period of cell division. In the growth period 
the spore mother-cells become differentiated from the general 
sporogenous tissues through a great increase in the amount of 
protoplasmic material. At some time in this growth period the 
nucleus of the spore mother-cell exhibits the phenomenon of 
synapsis, a very characteristic event, recognized by the very 
much contracted condition of the chromatin network in the 
interior of the nucleus. Synapsis is believed to hold fundamental 
relations to reduction phenomena as the time when chromosomes 
unite with one another in pairs. The period of cell division fol- 
lows synapsis and is characterized by two mitoses in the spore 
mother-cell, the second following immediately upon the first, and 
a segmentation of the protoplasm, sometimes by two successive 
divisions, and sometimes by a simultaneous cleavage, into four 
spores. The two mitoses present certain peculiarities in the 
structure and behavior of their chromosomes which are unlike 
the events of typical mitoses. The first is known as the hetero- 
typic and the second as the homotypic mitosis. These peculiar- 
ities have been recognized for a long time and have furnished 
the subject of much investigation and contradictory explanations. 
They were briefly described in Section III (Amer. Nat., vol. 38, 
P. 740, Oct, 1904) but recent studies of Farmer and Moore 
(: 03, : 05) have opened again a discussion which seemed closed 
at that time. The details of synapsis and the heterotypic and 
homotypic mitoses will be taken up under the caption, ** Reduc- 
tion of the Chromosomes.” 
Contrary toa statement in Section III of these studies (Amer. 
