in Lilium Martagon: II. Spermatogenesis. 215 
sufficiently remarkable. It must have some meaning. When 
an adequate explanation has been found, it will probably 
throw light on some of the problems of heredity. In the 
meantime we may define a difference which our knowledge 
is insufficient to explain. 
The homotype process of karyokinesis is illustrated by the 
series of diagrams A-F on Plate XI. This is an ideal series, 
representing what might be expected of an imaginary nucleus, 
which should divide like a vegetative nucleus (I, p. 451 and 
Figs. 1-8) while possessing only twelve chromosomes. 
Professor Strasburger has described and figured a sym- 
metrical arrangement of the coils in the spirem-form of nuclei 
from the endosperm of Fritillaria 1 . I am convinced that 
a similar arrangement exists in the much smaller vegetative 
nuclei of Lilium Martagon (B). The chromosomes when 
they first appear have a ribbon-like character, and retain 
traces of their late coiled arrangement in the spirem-nucleus 
(C). They contract and straighten out to a more regular 
form. Each is bent near one end which lies in the equatorial 
plane of the spindle. The other points to one of the poles. 
Longitudinal fission first appears in this stage (D). Later 
on the whole chromosome comes to lie more or less in the 
equatorial plane, and separation of the two halves begins 
at the end which is attached to the spindle (E). The diaster- 
segments are necessarily hooked (F). 
Each of the five homotypic divisions is now to be compared 
with the ideal series A-F. 
(1) The division of the micropylar nucleus in the binucleate 
embryo-sac agrees with it in all but two points. This nucleus 
when in the spirem-form, and also the young chromosomes 
of the succeeding stage, are apt to be pulled out in the 
direction of the future spindle, thus concealing the symmetry 
of the spirem-coils (I, p. 464 and Figs. 28, 29). Besides this 
deviation from the type there is. a second occasional variation. 
In a few chromosomes of the nuclear plate — one or two 
1 Strasburger, Ueber Kern- und Zelltheilung, 1888, pp. 61 63, Taf. II, 
Figs. 2 and 3. 
