84 U)iu'rrsif!i of ('oJifor)iia ri(J)li(afio)is in liofainj | Vol. 7 



most fniulaiiu'iital oiiloyciictiL' processes of tlie plant can be modified 

 l)v ciillural iiiHucnces. Field studies and garden eultiires, however, 

 do not support tlie suggestion, elsewhere rioted, that these transitory 

 or the other more deeply seated teratological variations are connected 

 with the time oi' appearance of the shoot during the growing season. 



An inherently abnormal rootstock, which may be expected always 

 to produce some abnormal shoots each season, must have had its origin 

 in a seed, since there is no evidence, on the one hand, that variations 

 induced in rootstocks l)y environmental ccmditions will recui- or, on 

 the other, that the individuals produced by offsets (asexual reproduc- 

 tion) ditfi'r in any way from the shoots formed from the parent root- 

 stock. This latter jooint has been thoroughly investigated in seeking 

 an explanation for the origin of the remarkable range of color forms 

 found in var. gigaiiieum. It is unfortunate that no one has grown 

 the progen.y of a teratological individual. It is apparent that among 

 the Eastern species certain of the abnormal individuals observed do 

 produce a little seed, and this is, I judge, especialW true of T. grandi- 

 florum var. variegatum. It is highly desirable that someone determine 

 the proportional occurrence of the variety and the normal form from 

 the seed of var. variegatimv. Unfortunately var. giganteum, even in 

 the case of entirely normal lowers, only rarely produces viable seed, 

 and thus it is probable that only the question of the recurrence of 

 teratological variations from the rootstock can be investigated. 



In general the initial production of the seeds giving rise to tera- 

 tological rootstocks can apparently be explained most readily on the 

 assumption that the parent plant was in a basically heterozygous con- 

 dition. The occurrence of abnormalities following hybridization, 

 especially in the case of wide crosses, is well recognized. A case some- 

 what in point is that of species Iwbridization in the genus Nicotiana, 

 in whi<'h the back-cross N. sylvestris X the F^ hybrid N. tahacum var. 

 macroplujlla X A. sylvestris yields a rather high percentage of very 

 abnormal individuals. In this connection it might be noted that the 

 wide range of color forms in T. sessile var. gigantciim seems best ex- 

 plained on the assumption of initial crossing of widelj^ differing forms, 

 an assumption perhaps borne out by the rather widespread sterility 

 in this variety. Finally, it should be borne in mind in connection with 

 this latter point that T. ovatum, which exhibits a relatively narrow 

 range of variability in flower color and in form and size characters 

 and rarely gives rise to teratological indi\i(luals. jtroduees an abund- 

 *ance of viable seed. 



