August 5, 1910] 



SCIENCE 



183 



He assumes that here also vacuoles are at 

 work, and by their extension and subsequent 

 collapsing produce all the movements which 

 constitute the whole process of nuclear divi- 

 sion, including the transportation of the 

 chromosomes from the equatorial plane to the 

 poles of the spindle and their subsequent as- 

 suming of the reticular condition in the rest- 

 ing nuclei. 



In describing his observations as shortly as 

 possible, we may start from the transportation 

 just named. Fischer assumes movements of 

 the granular plasm to account for this phe- 

 nomenon, whilst most cytologists invoke a con- 

 traction of the threads of the spindle. But in 

 Spinacia a longitudinal row of vacuoles is 

 seen between the two separating halves of the 

 chromosomes. Moreover, the spindle becomes 

 larger during this process, and not smaller, 

 as it should on the ground of the latter sup- 

 position. . Often the chromosomes separate 

 first at their free ends, instead of diverging 

 first at the points where they are united to the 

 threads of the spindle. This indicates the 

 swelling of the vacuoles between them as the 

 mechanical cause of their separation. 



After reaching the poles of the spindle, the 

 chromosomes at first constitute a compact 

 group, but this is soon distended. Vacuoles are 

 swelling between them; their walls are seen in 

 the shape of fine lines of linin, giving the 

 image of threads stretching from one chromo- 

 some to another. The swelling of these vacu- 

 oles is then seen to continue, they increase in 

 volume, come forth from amidst the chromo- 

 somes and finally surround them on all sides, 

 until their walls touch one another. In this 

 way a complex group is produced, the outer 

 walls of which combine to constitute the nu- 

 clear membrane, whilst the inner parts of the 

 walls either disappear or otherwise become 

 invisible. 



The chromosomes now change from the 

 compact into the reticular condition. They 

 do so by means of numerous very small vacu- 

 oles, which slowly increase in size, and thereby 

 distend the surrounding material. Each 

 of the chromosomes is changed in this way 

 into a network and the whole nucleus be- 



comes a " reseau de reseaux " as it has been 

 called by Gregoire. 



Wlen at the close of the reticular or resting 

 period the nuclei return to activity, all these 

 processes are, of course, gone through in the 

 opposite direction. First the chromosome- 

 vaeuoles collapse, thereby restoring the com- 

 pact condition. Then a longitudinal row of 

 vacuoles appears in each chromosome, indi- 

 cating the beginning of their division. After- 

 wards the nuclear vacuoles collapse, causing 

 the nuclear membrane to disappear. 



Even as in the petals of some colored flowers 

 colored and uncolored vacuoles may be seen 

 within the same cells, betraying different 

 physiological properties of the individual va- 

 cuoles, Mr. Stomps assumes different qualities 

 for his three main groups of vacuoles, viz., 

 chromosome-nuclear and spindle-vacuoles. 



The point in his description which will prob- 

 ably interest his readers most of all is the 

 explanation of the nuclear membrane as a wall 

 of numerous vacuoles, or a compound tono- 

 plast. 



In comparing the drawings and descriptions 

 of Strasburger and others and especially those 

 of Gregoire, with this new principle, it wiU 

 easily be seen that in the main they quite 

 well agree with it. The description of the 

 nuclear division in the roots of Allium by 

 Gregoire' may even be considered as good 

 corroborative evidence. On the other hand, 

 it is always hazardous to base a physiological 

 hypothesis on the observation of fixed and 

 stained material only. Experiments on the 

 behavior of the new nuclear vacuoles during 

 active life seem strongly required for a fully 

 reliable proof. 



Hugo de Vries 



I SPECIAL ARTICLES 



-J UNISEXUAL BROODS OF DROSOPHILA 



In an experiment begun at Columbia Uni- 

 versity in March, 1909, several pairs of pom- 

 ace flies produced broods consisting of males 

 only, or females only. The sexes of Droso- 

 phila usually appear in very nearly equal 

 numbers. Table I., A and B, gives the figures 



'La Cellule, T. XXIII., Fasc. 2, 1906. 



