728 THE AMERICAN NATURALIST. [Vol. XXXIX. 



mother-cell of certain angiosperms has emphasized these points 

 and Gr^goire 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 Capsella 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 chrbmosomes 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 



