The individuality of the chromosomes and their serial arrangement, etc. 117 



The Somatic Division. 



In entering the prophases, a nucleus enlarges slightly and the chromo- 

 somes increase in size. They retain, however, the same shape they had 

 in the resting nuclei. While increasing in size they separate somewhat 

 from each other and become quite evenly distributed against the nuclear 

 membrane somewhat as the bivalent chromosomes are placed in dia- 

 kinesis. They are also somewhat angular or even drawn out at different 

 points as if connected with each other by cross fibres from various direc- 

 tions (figs. 5 1) and 6). 



The chromosomes are at this stage almost isodiametric and their 

 shape does not itself suggest the trend of the series, still in many of the 

 nuclei in this stage of division the series can be followed at various places 

 for some distance. The connecting strands of linin are thin and are not 

 sharply differentiated from the chromatin by the stain. 



Judging from the frequent occurrence of this stage in sections of 

 root tips and young anthers, it must persist for some time. It may be 

 characterized as the growth stage, and in it the chromosomes make 

 their greatest visible increase in size. The resting nuclei range in diameter 

 from 4,5 to 6,75 /« with the chromosomes about 0,2 or 0,3 p in diameter. 

 In the prophase stage just described the nuclei are from 6,75 to 7,5 a in 

 diameter and the chromosomes are from 0,3 to 0,4 u in diameter. During 

 later stages of the prophases the nuclei enlarge but little. The chromo- 

 somes, however, appear to enlarge somewhat. The relative sizes at 

 various stages will be seen by comparison of figures 4, bb, 10, and 11. 



In passing from this stage the chromosomes move in from the peri- 

 phery of the nucleus and their apparent arrangement in a single con- 

 tinuous spirem becomes more clear. The spirem is variously twisted and 

 coiled about in the nuclear cavity. That it shows no breaks at all can 

 not, of course, be established. There may be several rather long and 

 more or less independent series. Figures la, 10, and 11 show several 

 stages in the appearance of the spirem during the early prophases. 



It is, however, clear in these nuclei of Car ex that the chromosomes 

 in resting stages and very early prophases do not primarily form a reti- 

 culum, but are connected in a series corresponding to the arrangement 

 in the spirem as seen in the mid-pro phase. The question as to the re- 

 lation of the chromosomes from the paternal and maternal parents in the 

 last previous fertilization is, of course, involved here and will be taken 

 up in connection with studies of the fertilization processes which I shall 

 report later. 



