No. 556] DEVELOPMENT IN NICOTIAN A 227 



tion occurs. These recurrent mutations, Johannsen says, 

 are rare in his experience, but they are admitted to occur 

 in almost any long-continued pedigree line, and if fasci- 

 ation should appear as a repeated mutation after 20 gen- 

 erations of plants involving 2,000,000 individuals had 

 been grown, is one to infer that the gene was present all 

 this time, but latent or inactive? Or is this a new gene 

 produced by the same condition that brought about the 

 original fasciation? Logically, if one defends the latency 

 conception, he must believe that the original gene for 

 fasciation was inactive in all these millions of plants, 

 which in our present stage of knowledge is a ridiculous 

 assumption, since the term is used to describe a somatic 

 appearance. Applied to genetic problems in general, 

 hopeless chaos would result. But on the supposition 

 that a portion of a chromosome is responsible for the 

 abnormality, it seems to me necessary to assume the 

 chromosome to be capable of becoming active or latent 

 without cause. For it seems probable that the anthers 

 are all alike from a constitutional standpoint. How else 

 can one account for the normal anthers and the abnormal 

 ones, the normal pollen mother-cells and those affected 

 by the abnormality? 



The conception of latency is not necessary in the case 

 of complete or incomplete dominance in Fj hybrids, for 

 in such cases there is evidence that a gene from one pa- 

 rent may be partially or completely inhibited in its ex- 

 pression by factors from the other parent, and this is 

 probably what happens when we bring a line of chromo- 

 somes and cell materials from the normal (402) pJants 

 and associate them (by fertilization) with a line of cell 

 materials from the abnormal (300-309). 



While the phenomena of segregation described in the 

 preceding pages may be capable of interpretation on a 

 morphological basis, the gene for fasciation appears to 

 me to lie deeper in sporogenesis than chromosomes. 

 The abnormal character development appears most 

 easily interpreted from a physiological standpoint. In 



