448 The Botanical Gazette. [November, 
Activity and function.—According to Guignard (10), at 
the beginning of nuclear division spheres migrate to the 
poles of the future nuclear spindle and then each one 
divides during the prophase of nuclear division. But ac- 
cording to those who hold that there is only one attrac- 
tion-sphere to the resting nucleus, the division takes place 
before the migration. Van der Stricht (29) finds that the 
division in the egg of Triton is, as a rule, effected in the qui- 
escent stage of the nucleus, rarely during the anaphase, and 
exceptionally during the metaphase. 
According to Heidenhain(151) every centrosome arises 
from another one, not by self-division, but by budding, the 
largest centrosome in a group being the oldest, and the small- 
est the youngest. 
The origin of the attraction-sphere and centrosome in the 
fertilized ovum does not seem as yet clearly worked out. As 
already stated, in the year 1888 Boveri advanced the opinion 
that the centrosome was brought into the attraction-sphere of 
the ovum along with the spermatozoon. But Guignard (10) 
found in the cells of the embryo-sac of Lilium Martagon that 
the attraction-sphere contained a centrosome before fertiliza- 
tion; so the hypothesis of Boveri must be given up. Accord- 
ing to Guignard (11) there is a union of the attraction-spheres 
and their contained centrosomes accompanying the conjugat- 
ing nucleus of the pollen-tube, with those of the nucleus of the 
embryo-sac during fertilization. He says that in angiosperms 
the two spheres brought with the male nucleus unite wit! 
the two of the female during the fusion of the two nuclei, 
leaving the new nucleus with two spheres, each composed 0 
a male centrosome and its sphere united with similar bodies 
from the female. 
cell organ—the attraction-sphere with its centrosome. 
organ propagates itself by division when the -cell does, 
the division of the sphere precedes that of the cell. The ray® 
of the spindle are attached to the sphere and are contractile 
fibers which attach themselves to the chromosomes and draw 
their halves towards the poles. The contractile rays of the . 
spindle obtain a firm hold, for the spheres are held in place 
