204 



THE CELL AND PROTOPLASM 



these forces are attractive at long' distances 

 even between like particles. The ("iifficulty 

 is to explain why, in meiosis, chromosomes 

 pair and in their pairing come together so 

 as to bring all the corresponding parts 

 into contact. At first sight it seems impos- 

 sible to postulate a mechanism of any 

 physical character to account for this, but 

 a consideration of the mutual energy of 

 configurations may throw some light on it. 

 The chromosomes are known to consist of 

 alternate segments containing more or less 

 nucleoprotein, the width and order of suc- 

 cession of which is its specific character. 



Now the energy of interaction between nu- 

 cleoprotein parts of chromosomes and non- 

 nucleoprotein parts is bound to be differ- 

 ent. If we make the reasonable assumption 

 that this energy of interaction depends on 

 the products of some character of the parts 

 interacting divided by some function of the 

 distance betw^een them, then we have for 

 the energy interaction between two nucleo- 

 protein parts the value -a^f{r); for two 

 non-nucleoprotein parts, -l>~/f{r); and 

 for a nucleoprotein part and a non-nucleo- 

 protein part -ah/fir), where a and h 

 stand for a specific coefficient of the nu- 



FiG. 4. Diagrams illustrating the approach of chromosoiues in such a way that corresponding parts 

 join. In Fig. 4A the long-distance force between the similar shaded segments at the left is «-//('•); 

 ijetween the similar unshaded parts at the right, b'^fir), where r is the distance between the segments. 

 Therefore the total force between the two nucleoprotein parts of two chromosomes is (a2 + fea) //(,•). 

 In Fig. 4B the force between each pair of non similar segments is ah/f(y), and the total force is 2ab/ 

 /(r). In Fig. 4C two chromosomes aic near together, hut since corresponding i)arts are not adjacent 

 the reaction is weak. In Fig. 4D the corresponding parts nf tlie clirdinosduie arc adjacent and the re- 

 action is strong. Fig. 4E shows first stage of apjiroach in wliicli tlie large nuclei are coming together. 

 Fig. 4F shows detailed ai)p(isiti(in of a region of small iiiiclci ami dtliei- lai-gi' rcgiims ctuuiug together. 



