THEORY OF PANGENEIC INTERCHANGE 237 



diagrams of Fig. 134 to illustrate what is meant by the above 

 theory of pangeneic migrations. We will suppose that the 

 parents of a hybrid have four pairs of contrasting characters, 

 namely, flowers terminal, flowers lateral, flowers blue, flowers 

 yellow, stems smooth, stems hairy, leaflets short, leaflets long, 

 and that the hybrid offspring all have lateral, yellow flowers, 

 hairy stems and short leaflets, these characters being dominant 

 and those contrasting with them recessive. Let us suppose 

 that when the cross-fertilization took place, the sperm cell con- 

 tributed but one chromosome and the egg cell but one; then in 

 the hybrid when the grandmother cells of the microspores and 

 megaspores enter upon the prophases of their first division 

 the paternal and the maternal chromosome would be found in 

 juxtaposition, either side by side as showii at E, Fig. 134, or end 

 to end. In this position there would be a chance of an inter- 

 change of pangenes (the paternal chromosome is shown black 

 and the maternal white). Then the chromosomes would be 

 drawn to opposite poles, and there each would split longitu- 

 dinally into two equal pieces, and these in turn would be drawn 

 to opposite poles (Figs. F, G, and H) to form the nucleus of the 

 spores, namely, two paternal and two maternal spores. 



Let us now consider more in detail the interchange of pangenes 

 that might take place in the prophase at E. At I is shown dia- 

 grammatically the two chromosomes of E, each chromosome 

 represented as consisting of two ids, and each id as composed of 

 two pangenes. The stippled chromosome is paternal and the white 

 one is maternal. Let us suppose that at the time of pangeneic 

 interchange the pangenes bearing flower color changed places as 

 indicated in I, and then that the chromosomes separated and 

 went through the steps of spore formation as shown in F, G, and 

 H, and, supposing that the same interchange takes place in the 

 mother cell of megaspores as in that of microspores, the result 

 H would be reached for megaspores also. Now, since the 

 characters possessed by the microspores and megaspores are 

 handed down to their sperm cells and egg cells respectively, 

 sperm cells Aj and A2 would be formed from microspores i and 2 



