354 
Mot tier. —The Effect of 
one-third to one-half the diameter of the nucleus before its 
membrane is ruptured and the nucleolus escapes into the 
cytoplasm. Sometimes the beak is drawn out into a long 
slender neck (Fig. 13). Such a condition is met with chiefly 
in the rapidly elongating cells of the central cylinder, but it 
may also happen in similar cells of the cortex. As a rule the 
nuclear membrane is ruptured sooner, so that only a short 
beak is formed. In the same section of a root-tip of Zea^ 
Phaseotus , and others, every conceivable transition between 
Figs. 12 and 13 may be seen in the plerome-cylinder. 
It is, however, only when the cytoplasm offers a consider- 
able resistance to the movement of the nucleus that the 
nucleolus can be made to fall through the membrane of the 
former. If the nucleus is able to move more freely within 
the cytoplasm, as is generally the case except in elongating 
cells of the plerome, it readily sinks to the lower end of the 
cell, resting against the end wall, when an expulsion of the 
nucleolus is impossible. In the rapidly elongating cells of 
the plerome the nucleoli seem to be larger and heavier than 
those in the adjacent region of the periblem. 
The linin-reticulum, if containing only a relatively small 
quantity of chromatin, as in Fig. 13, will experience little or 
no displacement. As a rule, the reticulum or nuclear thread is 
displaced in a certain degree along with the nucleolus even in 
embryonic cells. The nucleolus is generally accompanied, 
when displaced, by the colourless area or sphere in which it 
often lies in the resting nucleus, a fact so noticeable in Zea . 
Sometimes, when the nucleolus is forced out of the nucleus as 
in Fig. 13, the former does not come into contact on all 
sides with the cytoplasm, but may lie within a colourless 
space. 
Since the colourless fluid surrounding the nucleolus does not 
retain any stain, it cannot be said with certainty that it is 
carried along with the latter. The facts seem to indicate, 
moreover, that the specific gravity of this colourless sphere is 
greater than that of the remaining part of the nuclear sap, 
and that it may be of a more viscid nature. In Allium , and 
