138 MR A. ANSTRUTHER LAWSON ON 
points which are directly opposite one another, so that the spindle is bipolar from its 
inception. ‘This is also true in some cases for the heterotype spindle, but as a rule in 
the latter, the weft of kinoplasm pushes out at a number of places and the fibrils converge 
at several points which are not necessarily opposite one another. The result is that a 
number of fibril sheaves are developed which are of conical shape, and the spindle at 
this prophase may be tripolar, quadripolar, or multipolar. By the coalescence of these 
cones, however, the spindle eventually becomes bipolar and has the same symmetrical 
form as the somatic spindle. With the organisation of the cones in the prophase— 
whether the spindle is bipolar or multipolar—it is believed that the nuclear membrane 
breaks down and disappears. The fibrils of the spindle now push into the nuclear area, 
and with their free ends become attached to the chromosomes. The latter become 
arranged at the equator, forming the characteristic equatorial plate, and we now have 
what is known as the metaphase. Hach bivalent chromosome separates into two 
daughter chromosomes, each of which moves to opposite poles of the spindle. It is 
believed by some cytologists that it is the contraction of the fibrils attached to the 
chromosomes which accomplishes not only the separation of these bodies, but also the 
migration of the two halves to the poles. 
These, in brief, are the conclusions reached by many investigators whose observations 
have extended over a wide range of types of vascular plants. They are the views that are 
commonly held at the present time, and they have in the main been sustained by the 
recent work of Farmer and Dicpy (1910). These writers, however, have done more. 
They have drawn some theoretical conclusions from their observations in an attempt to 
account for the factors concerned in the various changes and movements in the cell 
expressed in the achromatic figure. Following the work of Professor Marcus Harroe, 
they have come to the conclusion that an explanation of these changes and movements 
may be found in the electrical conditions of the cell. They point out the remarkable 
manner in which the sheaves of fibrils, during the prophase, diverge in the proximity 
of the chromatin-charged linin, and that these are so repelled by each other that they 
press out equidistantly at the periphery of the cytoplasm. This condition appeals to 
them as convincing evidence in support of their hypothesis that the linin, with its 
contained chromatin, by virtue of the chemical changes involved in its metabolism, has 
brought about an electrical condition of opposite sign, similar in each of the spindle 
cones. This hypothesis seems to them to be in harmony with the fact that the dis- 
appearance of the nuclear membrane is closely associated with the spreading of the 
chromosomes beneath it just before their retrogressive movement to the equator, whilst 
the spindle poles have shifted away from the nuclear surface. For these and other 
reasons Professor Farmer lends his support to the view that electrical conditions in 
the cell are not only responsible for the form of the spindle, but for its very existence 
a view frequently put forward, but not generally accepted. 
Without attempting an analysis of this hypothesis, I should like to point out some 
difficulties which I have experienced in interpreting the observations which have been 
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