Foundations of the Mutation Concept. 7 



chromosomes and two with only 6. The same irregularity lias 

 since been seen in various other types. There can be no reasonable 

 doubt that lata originates in this way, through the union of a germ 

 cell having 8 with one having 7 chromosomes, unless we deny some of 

 the best established facts in cytology. Stomps, however (1916), 

 goes so far as to deny the probability of this hypothesis, although 

 he does not venture to offer anything in its place. His denial is 

 based on the fact that several mutant types are known to have 15 

 chromosomes. But, as has been pointed out, 1 if the 7 

 gametophyte chromosomes are unlike, as is probable from many 

 general cytological considerations, then 7 distinct types with 15 

 chromosomes are to be anticipated. Up to the present, no such 

 number of forms having 15 chromosomes has been described from 

 any strain of (Enothera, nor have seven such forms been 

 authenticated altogether, although there is no obvious reason why 

 they should not ultimately be found. 



The evidence, then, is clear and definite that lata originated 

 through a chromosome entering the wrong nucleus in the reduction 

 division. In this way two pollen grains, or one megaspore will be 

 produced, each having 8 chromosomes in its nucleus. The presence 

 of the extra chromosome, as a duplicate of one, will no doubt 

 immediately have its effect on the cytoplasm of the pollen grain or 

 megaspore containing it. So that the mutation must quickly 

 become a property of the cell as a whole, and, theoretically, at 

 least, this will alter the character of the whole male or female 

 gametophyte derived from a spore with 8 chromosomes, though the 

 differences may not always be demonstrable by the microscope. 

 Rentier (1919) has shown that visible differences exist between the 

 pollen grains and male gametophytes of various species, and that 

 segregation of these characters takes place in the pollen of the Fj 

 hybrids. If an egg from a mutated megaspore has 8 chromosomes, 

 it is already different both in nucleus and cytoplasm from an 

 ordinary egg of the type, since the extra chromosome has been 

 producing its effect thoughout all stages of the embryo-sac formation. 

 Nevertheless, the only original change which it is necessary to 

 assume, to account for the appearance of lata, is a chance irregularity 

 in which both members of a pair of chromosomes enter the same 

 nucleus in the reduction division. To endeavour to explain the 

 origin of (E. lata through an alteration in a hypothetical pangen 

 when the visible facts of the chromosome structure are so clear, is to 

 desert science for obscurantism. 



> Gates, 1915, p. 181. 



