
728 THE AMERICAN NATURALIST. ` (VoL. XXXIX, 
mother-cell of certain angiosperms has emphasized these points 
and Grégoire and Wygaerts (:03) have also shown the difficul- 
ties of following the chromosomes in the resting nuclei of the 
root tip and spore mother-cell of Trillium, stating that the struc- 
tures become resolved into an alveolar network. 
On the other hand Rosenberg (:04) claims that the chromo- 
somes may be clearly recognized in the resting nuclei of some 
forms and cites Capse//a bursa-pastoris as a particularly good 
illustration. In this plant the chromosomes are described as 
small granular bodies scattered throughout the nucleus in fixed 
number at various stages of ontogeny. Thus there are 16 in 
cells of the gametophyte and 32 in those of the sporophyte 
while 48 of these bodies were counted in the nuclei of the endo- 
sperm as would be expected if these nuclei are descendants of a 
triple fusion in the embryo-sac. Similar conditions are reported 
in other forms and there is considerable evidence giving weight 
to the view that chromosomes may be actually followed through 
all periods of the nuclear history in some favorable types. 
Apart from the actual demonstration of the chromosomes in 
the resting nuclei and their recognition as structural entities 
through successive cell divisions there is much general evidence 
in support of the theory of the individuality of the chromosomes. 
This evidence lies in the nuclear fusions of fertilization and the 
mitoses of processes of segmentation that follow where the 
chromosomes are known to remain separate and have been dis- 
tinguished as maternal and paternal. Also, as we have seen 
from the discussions of reduction phenomena at sporogenesis 
and the behavior of the chromosomes in hybridization, there are 
good reasons for believing that maternal and paternal chromo- 
somes remain separate all through the sporophyte generation 
and are distributed to the offspring during sporogenesis. The 
Importance of these events in the minds of all investigators has 
rested very largely on the behavior of the chromosomes and has 
led to the very general assumption that they must stand for 
units of organization and may be counted as constant factors in 
the problems of heredity. It is not necessary to adopt Boveri's 
extreme views to hold still the theory of the individuality of the 
chromosomes. Nor is it necessary to assume that the structures 
