1921} SHOW ALTER—CHROMOSOM ES 247 
become apparent until very late; in fact, it is perceptible only 
when the separation of the daughter chromosomes has actually 
begun (figs. 13-15). The chromosomes are in the form of bent, 
crinkly rods of varying lengths (figs. 1-11). The crinkliness is 
less apparent in the late metaphases and in the anaphases when 
the chromosomes are drawn out into smooth rods (figs. 12, 16, 19). 
As observed by Escoyez,‘ they occupy a very definite plane in the 
equatorial plate stage; in polar view they are easily counted at 
this time, but in lateral view they appear as tangled masses 
(figs. 8, 14, 15). Only one case (fig. 11) was found of an equatorial 
plate stage in which the individual chromosomes could be traced 
with any degree of certainty in a lateral view, and a very few such 
cases in anaphases (figs. 12, 16, 19). The chromosome number is 
plainly nine in either sex (figs. 1, 2, 4, 9, and 18 female; figs. 3, 5, 
6, 8, and 1o male), one of the chromosomes being very small. 
This small chromosome shows no constant difference in behavior 
from the other chromosomes, either as to its position on the spindle 
or in its time of division. In one case (fig. 15) it was found to 
have been divided earlier than the other chromosomes, and in 
another case it was found undivided in the equator of the spindles 
when the other chromosomes were in anaphase (fig. 19). Meta- 
phases and anaphases in which the individual chromosomes are 
distinguishable are very rarely found, but if the small chromosome 
constantly led the way in division, as it appears to do in fig. 15, 
or if it constantly lagged, as seems to be the case in fig. 19, it should 
usually be visible in the metaphases and anaphases, even though 
the other chromosomes are not distinguishable one from another. 
Apparently the small chromosome ordinarily divides at about the 
same time as the other chromosomes, and in lateral view is dis- 
tinguishable from them only in rare cases (figs. 12, 15, 16). 
In cells of the apical tip of the thallus (of either sex) in which 
the chromosomes are commonly spread out so as to make accurate 
counts possible, the small chromosome is visible in about 80 per 
cent of the cases counted; but in the antherid, where the cells are 
much smaller and the chromosomes generally more closely grouped, 
4Escoyez, E., Blepharoplaste et centrosome dans le Marchantia polymorpha. 
La Cellule 24:247-256. 1907. 
