50 White. 



3. Fasciation and environment 95 



4. Fasciation and selection 100 



5. Fasciation and hybridization 103 



a) Fasciation X normal 103 



h) Fasciation X calycanthemy 114 



6. Summary and conclusions 119 



G. General discussion, showing the bearing of these data on certain 



general problems of heredity and evolution „ 128 



Table 1-26 ,135 



A. lutrodiictiou. 



The present paper is the outcome of an extended series of studies 

 on the phenomenon of fasciation in plants. The first part consists 

 largely of compiled date on its occurrence and classification, together 

 with a review of the researches of de Vries on this anomaly. In the 

 second part, I have described in some detail, a series of hybridization 

 experiments, in which a mutant variety of Nicotiana tahacum breeding 

 true to fasciation was crossed with several distinct normal varieties of 

 this same species, as well as with several strains belonging to markedly 

 distinct species. In the course of this account, I have tried so show 

 the necessity of dispensing with the latent character conception of the 

 morphologists and of being more precise in our use of terms. Particular 

 emphasis has been laid upon the fact that a character always is the 

 result of both internal and external factors and hence non-existent as 

 a continuous entity in the germ-plasm of two or more successive gene- 

 rations of organisms. Characters are either present or absent and 

 never latent. Characters morphologically indistinguishable, and present 

 in the same species of organism, may be entirely unrelated when viewed 

 from the standpoint of cause. Such facts have a very important bearing 

 on the numerous morphological studies of evolution which the last half 

 century has brought forth. Many of the morphological studies concerning 

 the origin and relation of various plant and animal groups must be 

 reinvestigated from this standpoint before the final word as to their 

 place in the evolutionary scale can be said, for it is obvious that a 

 plant with a character caused by a combination of a certain protoplasmic 

 material with a certain environment is not necessarily even remotely 

 related to an organism with the ^anie character produced by a different 

 kind of protoplasmic material in a different or perhaps even the same 

 environmental medium. 



