142 MR A. ANSTRUTHER LAWSON ON 
It is believed by some that the meaning and function of the achromatic figure is to 
accomplish the separation of the chromatin substance of the mother nucleus into two: 
equal portions. It is believed that by the contraction of the fibrils which undoubtedly 
become attached, the daughter chromosomes are not only separated from one another, 
but are actually pulled to opposite poles of the spindle. Here again I find some 
difficulties. In the first place, the poles of the bipolar spindle rarely extend as far as 
the cell-wall, and consequently if such actual pulling of the chromosomes takes place, 
there appears to be no stationary resistance to pull against. And then again, from an 
examination of many preparations I find that the daughter chromosomes invariably 
pass beyond the region of the pole of the spindle. These and other facts do not lend 
support to the idea that this movement is accomplished by the contractility of the 
connected fibrils. 
And finally the question presents itself: If these fibrils of the achromatic spindle 
have no concern in the separation of the daughter chromosomes, what is the reason for 
the existence of such a complicated mechanism ? 
In view of the many difficulties and inconsistencies mentioned above, is it not — 
possible that the development and function of the achromatic figure have been mis- 
interpreted? Is it not possible that the so-called ‘‘mechanism of mitosis” represents 
the passive results and effects of movements rather than an active agent in such 
movements? After a careful, comprehensive study of a wide range of types, I am 
forced to answer these questions in the affirmative. I have also been convinced that 
the cause of so many difficulties lies in the fact that a series of important and critical 
stages in spindle formation has been overlooked—stages which throw an entirely new 
light on the problem, and which will necessitate a revision of the accepted views and 
interpretations of nuclear phenomena. 
These stages are to be found in the later prophase, preceding the organisation of 
the equatorial plate. ‘They are stages concerning the fate of the nuclear membrane. 
Contrary to my earlier observations, as well as to the observations of the majority of 
cytologists, I find that the nuclear membrane does not break down, but, on the contrary, 
behaves as a permeable plasmatic membrane should behave under varying osmotic 
relations. The discovery of these stages not only clears up a doubtful point which I 
mentioned above in regard to the prophase, but is far-reaching in its importance. It 
goes to prove that osmotic conditions rather than electrical conditions are active factors 
concerned in the formation of the achromatic spindle. ‘This I shall attempt to 
demonstrate from a study of the spore mother-cell of Disporum, Gladiolus, Yucca, and 
Hedera, also the vegetative cells in the root tip of Adliwm. 
DIsPoRUM. 
In fig. 1 we have represented a median section of a microspore mother-cell of 
Disporum Hookeri. It is taken at a time when the nuclear cavity is just about its 
maximum size, soon after the growth period, which up till recently was known as 
