132 Arlow Burdette Stout 



chromosomes; Clemens Muller (1909) for Yucca aloifolia, Yucca 

 Draconis, and Yucca guatemalensis, various sizes of large and small 

 chromosomes; Rosenberg (1909a) for Crepis wrens, two small, two 

 large, and two intermediate in size; Tahara (1910) for Crepis japonica, 

 sixteen chromosomes of various sizes; Ishikawa (1910) for Ginkgo biloba, 

 twelve bivalent chromosomes of which one pair is large. There is also 

 a vast literature regarding heteromorphism among chromosomes in ani- 

 mals, regarding which adequate summaries have been given by Stevens, 

 Wilson, and Montgomery. 



The chromosomes of Carex aquatilis are at their maximum develop- 

 ment small bodies. They certainly are slightly, if at all, larger than 

 the so-called chromomeres appearing in the spirem of the prophases of 

 many plants. On this point I have made comparisons of the chromo- 

 somes as they appear in figures 10 and 11 with the spirem appearing 

 in the prophases of the onion. The chromosomes in Carex at this stages 

 are about 0,5 a in diameter, while the spirem of the onion is not less than 

 0,8 jm in diameter. The diameter of the spherical chromosomes is, there- 

 fore, somewhat less than the thickness of the spirem in the onion at 

 the time when the latter first shows the longitudinal split. 



As far as I can observe the chromosomes in Carex aquatilis are ho- 

 mogeneous bodies. At no time during the somatic divisions do they 

 appear to be made up of smaller units, "chromomeres", or "ids" as parti- 

 cularly conceived by Weismann (1892) and Strasburger (1894). On 

 this point the appearance of the chromosomes during somatic division 

 is most interesting. As already described in detail, the chromosomes 

 are at all stages of the prophases spherical or oval bodies. At no time 

 is their substance drawn out into a series of "ids" which may be divided 

 equally by a longitudinal split. The division of the chromosomes is 

 quantitative, but unless the entire chromosome is of uniform composition, 

 it is difficult to see how the division can be equational. 



In marked contrast to this constantly compact organization of the 

 chromosomes of the somatic nuclei are the conditions seen in synapsis. 

 Here the chromosomes are spun out at great length into a fine thread, 

 the folds of which are intricately interlooped together. Out of this a 

 continuous pachynema thread develops and from this a double series 

 of chromosomes is formed. 



The opportunity for the exchange of actual substance between the 

 paternal and maternal germ-plasms during such a union are very great 

 and the various possibilities that exist in such a case are well presented 

 by Allen (1905). He points out and discusses the following possibilities ; 



