Graham. — Niiclear Division of Preissia commutata . 663 
gradually lose their irregular outline and become distributed on the linin in 
the form of chromomeres. Gregoire and Wygaerts (’ 03 ) believe that 
there is no distinction between linin and chromatin, that it is but one sub- 
stance. They look upon the smaller dense bodies in the nucleus as chro- 
matin and the network as a thinner part of the dense bodies, that lies 
between them. The nuclei in Preissia commutata are so very small that i*t 
is impossible to say whether the reaction of the dense bodies is unlike the 
reaction of the filaments when triple stain is used. The nuclei in the Liver- 
worts are so small that they are not favourable objects for the study of this 
question. When the spireme is first formed it is narrow, and the chromomeres, 
which are very conspicuous at this stage, appear on it at unequal distances 
(Figs. 3, 4, 5). Later, when the spireme thickens, the chromomeres are 
not distinct (Figs. 9, 10, 13, 14). This account of the formation of the 
spireme in Preissia commutata agrees, in general, with the account of the 
formation of the spireme in higher plants, as described by Farmer and 
Shove (’ 05 ) in the vegetative cells of Tradescantia virginica , and by Wager 
(’ 04 ) in cells in the root-tip of Phascolus and others. Coincident with its 
formation, there is a general contraction of the spireme from the periphery 
of the nucleus towards the nucleolus (Figs. 4, 5). The spireme finally 
contracts so closely about the nucleolus as to almost hide it (Fig. 6). Finer 
linin threads extending from the contracted spireme to the periphery of the 
nuclear membrane may also be seen in this figure. This contraction is 
a conspicuous stage in the mitosis of the vegetative cells of Preissia 
commutata , and has been observed in the germinating spores of Pellia 
epiphylla by Davis (’01), who calls it synapsis, and in Carex by Stout (’ll). 
Later the spireme moves away from the nucleolus. At this time it is very 
uneven, being slender in some places and thick and jagged in others 
(Figs. 7, 8). These uneven regions disappear, and a spireme of uniform 
consistency comparable to that found in the higher plants by many 
students lies loosely coiled in the nuclear cavity. This spireme appears to 
be continuous. Chromomeres, so conspicuous in the early stages of the 
spireme, cannot now be distinguished readily. An unsegmented spireme in 
the vegetative division of the Liverworts has been mentioned several times, 
but up to the present time has not been fully described nor illustrated. 
This may be due to the fact that little work on the cytology of these plants 
has been done. Van Hook ( 00), who studied the vegetative cells of 
M archantia polymorpha in the stalk of the archegoniophore, says that he 
did not observe a spireme. Davis (’01) says that the linin and chromatin 
in the germinating spores of Pellia epiphylla form a broad spireme. 
Chamberlain (’ 03 ), who also studied the germinating spores of Pellia 
epiphylla , states that the nuclei elongate after the spireme is formed. Neither 
of the last two investigators figured the spireme. 
That there is a contraction of the spireme may be objected to on the 
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