134 Arlow Burdette Stout 



ment may be the normal condition in resting nuclei and that the reti- 

 culated appearance commonly observed is an artefact. Flemming (1882) 

 in considering this point reinvestigated the nuclei of Chironomus larvae 

 and verifies Balbiani's observations as to the presence of a chromatic 

 spirem. He remarks that in these cases the organization of the resting 

 nuclei is very similar to that at the beginning and the end of nuclear 

 division. 



Rabl's (1885) conception of polarity in the nuclei of the salamander 

 is based on the uniform and constant convergence of the spirem loops 

 toward the polar field. He clearly shows that although the chromosomes 

 give off anastomosing branches there are in the reticulum traces of the 

 boundaries of the chromosome loops. He points out that this is evidence 

 for the individuality of the chromosomes. A study of his figures shows 

 also that the serial arrangement of the chromosomes seen most clearly 

 in the spirem can also be traced with considerable clearness in these rest- 

 ing nuclei. 



A classical example of the intimate association of chromosomes in 

 series is seen in Ascaris megalocephala Uvalens. Here there are long 

 chromatin rods which behave like individual chromosomes in the germ 

 cell divisions, but in somatic divisions each breaks up into about twenty 

 segments which are to all appearances chromosomes. Edwards (1910) 

 has shown that in Ascaris lumbricoides the so-called sex element of the 

 maturation divisions is a group of five chromosomes. Other evidence 

 similar to the above shows that chromosomes may be associated in series 

 making what may be called plurivalent chromosomes. The condition in 

 Carex aquatilis is somewhat similar in that in the prophases of the reduc- 

 tion division the chromosomes are connected up in a homogeneous spirem 

 quite as they are in the embryonic divisions of Ascaris. 



Since Strasburger (1905) reported the presence of paired chromo- 

 somes in dividing diploid nuclei in Galtonia and Funkia much evidence has 

 appeared to show that such an arrangement of the somatic chromo- 

 somes is present in many plants. This pairing may be so intimate that 

 each pair appears as one double chromosome, a condition shown by Over- 

 ton (1909, p. 23). Other cases of constant pairing in somatic nuclei 

 have been reported, especially by Clemens Muller (1909) in various 

 species of Yucca; Rosenberg (1909a) in Crepis virens and (1909c) in 

 Drosera; Gates (1911) in Oenothera; Stomps (1911) in Spinacia. 



I shall not here discuss the much disputed question of end to end 

 or side by side association of homologous chromosomes during synapsis. 

 The evidence is, I believe, conclusive that a paired condition is a feature 



