20 INTRODUCTION. 
represents a slight pause in the process of mitosis. For this reason it 
is the stage most easily obtained and most frequently observed. 
METAKINESIS. 
Up to the stage of the mature spindle, as in Fig. 7, H, each 
chromosome is seen to consist of two daughter segments oriented in 
one of the ways described above. As soon, however, as these seg- 
ments begin to separate in metakinesis, each splits longitudinally in a 
plane at right angles to the longitudinal splitting which took place in 
the prophase. In some instances, and when the chromosomes are 
viewed from the end, each is seen to be composed of four rods, the 
four granddaughter segments, placed side by side in pairs, forming a 
tetrad, Fig.9, A. As a rule the granddaughter segments cannot be 
definitely recognized until the daughter segments have separated 
somewhat. Having almost or quite separated, the daughter segments 
are seen to be in the form of a V, although it never should be for- 
gotten that V’s do not invariably result. As the result of the second 
longitudinal splitting, each typical V-shaped daughter chromosome 
consists of two granddaughter segments which adhere or are even 
fused at the ends to which the spindle fibers are fastened, while the 
opposite ends diverge (Fig.9, B). It frequently happens that the 
opposite ends of the granddaughter segments do not diverge, but lie 
more or less in contact side by side, so that the retreating daughter 
chromosomes consist of two applied rods (Fig. 9, F, the middle pairs). 
In some cases, as already mentioned, the ends of the granddaughter 
segments forming the angle of the V fuse, so that the V appears to be 
one piece formed by bending. The bent or contorted condition of the 
granddaughter segments during ‘metakinesis is due to the previous 
twisting of the daughter chromosomes upon each other. 
If the chromosomes be in the form of rings, as shown in Fig. 8, E, 
it is evident that the separating daughter chromosomes may also be in 
the form of a V or U, but such V’s and U’s will be produced by a 
bending of the daughter segments. This is true in a great many cases 
in £L2lzem and in other plants, among both monocotyledonous and 
dicotyledonous species. In such cases each U or V is invariably 
double, as the result of the second longitudinal fission—that is, the 
granddaughter segments are U-shaped and closely applied to each 
other (Fig. 9, F, right and left). Sometimes these granddaughter seg- 
ments may separate slightly, giving the impression of two similar 
daughter chromosomes lying one just beneath the other. This is one 
of the several phenomena that have led to erroneous interpretations 
of the chromosomes. 
