The individuality of the chromosomes and their serial arrangement, etc. 133 



(1) Complete fusion of homologous idioplasms followed by equational 

 division; (2) Partial fusion followed by equational division of fused por- 

 tions and a varying distribution of uncombined portions; (3) No actual 

 fusion, but mixture of the homologous idioplasmic units with redistribu- 

 tion of the various elements; (4) Rearrangement of entire chromosomes 

 as units; (5) Interaction (perhaps chemical) between non-fusing portions 

 of idioplasm; (6) Such a separation after contact of fusion that "each 

 germ-cell receives the pure idioplasm of one or the other parent". 



It would appear that the various possibilities for exchange and 

 mutual influence during synapsis may be sufficient to account for the 

 observed facts of heredity without assuming that there must be a chance 

 distribution of chromosomes during the heterotypic division. 



The serial association of the chromosomes has a significant bearing 

 on the problems as to the general organization of the nucleus. Evidence 

 against the existence of a continuous chromatic spirem at any stage has 

 been brought out by Martins Mano (1905), Gregoire (1906), Overton 

 (1909), Stomps (1911) and others. 



Martins Mano (1905) and Gregoire (1906) hold that in various 

 species of Allium, and in Solanum tuberosum and Phaseolus vulgaris 

 there is no spirem, either continuous or segmented at any stage of the 

 somatic divisions. They further hold the view that there is no distinc- 

 tion between linin and chromatin, but this contention has not been ac- 

 cepted, at least as having general significance. 



Overton (1909), however, in his studies of the pollen mother-cells 

 of Thalictrum purpurascens, Calycanthus floridus and Richardia africana 

 finds that the prochromosomes in resting somatic and sporogenous nuclei 

 are arranged in parallel pairs with obvious linin intervals, and holds 

 that "these heterogeneous spirems probably remain distinct throughout 

 the life history of the sporophyte". In his more recent studies on Podo- 

 phyllum peltatum (1911) he also emphasizes the fact, that while the spirem 

 of the prophases is not a continuous chromatic spirem, the chromosomes 

 are connected by visible linin intervals into a definite spirem. 



Stomps (1911) on the other hand reports that in Spinacia oleracea 

 there is no serial alignment of the chromosomes and that the chromosomes 

 even pass through synapsis without any evidence of a continuous serial 

 arrangement. 



In the older literature conspicuous cases of the presence of a chromatic 

 spirem in resting nuclei are reported for the gland cells of Chironomus 

 (Balbiani, 1881) and the epithelial cells of various other insects (Van 

 Gehuchten, 1890). Balbiani even suggests that the spirem arrange- 



