138 CARNEGIE INSTITUTION OF WASHINGTON. 



vestigation of the inheritance of green cones and of doubling is being 

 continued by Dr. Blakeslee. In view of the technical difficulties of 

 hybridization, the decrease of vigor, and the increase of intersterility 

 due to inbreeding, and on account of the loss of the special knowledge 

 and technical skill for this work which followed the death of Mr. 

 Avery, it seems desirable to discontinue for the most part further 

 work with these forms. 



In the portulacas, Dr. Blakeslee is carrying out further experiments 

 with the dwarf mutation, which has been shown to be a Mendelian 

 recessive, and with the reverting normal branches which they occasion- 

 ally produce, which have been shown to be heterozygous dominants. 

 An attempt is being made to alter the proportion of reverting branches 

 by external stimuli. A number of vegetative mutations have also been 

 found in flower colors, recessives mutating to dominants. The portu- 

 lacas show a wide range of color in their flowers and give an oppor- 

 tunity to study color inheritance in this species, which is being availed 

 of. Thus the portulacas reveal again that extraordinary richness in 

 biotypes of plant species which Dr. George H. Shull years ago demon- 

 strated at this station in the case of the wild shepherd's purse, a species 

 which was commonly regarded by botanists as a unique representative 

 of the genus in America. 



Research on the variability in the jimson weed (Datura) is being 

 resumed. The following mutants have been studied and named: 

 Globe, Round-leaf Globe, Cocklebur, Poinsettia, Buckling, Sugarloaf, 

 Polycarpic, Microcarpic, Ilex, Glossy, Rolled, and New Species. In 

 addition, a number of new mutants as yet unnamed have been dis- 

 covered and are being investigated. In one of the mutants an aber- 

 rant color ratio has occurred. 



Of the cross between a weeping and an erect mulberry, the F2 

 generation in the field is ready to be recorded. The weeping char- 

 acter appears to be a simple INIendelian recessive. Some of the Fi 

 plants which were last season recorded as male, this season produced 

 both male and female flowers. Not all the Fi plants were in flower, 

 but in another season it should be possible to obtain sex-ratios in the 

 Fi generation. 



In poplars we obtained last spring flowers from Fi plants of a cross 

 between an erect and a weeping aspen and have a few F2 seedlings now 

 in the nursery. 



This summer, flowers were produced in Fi plants of a cross between 

 the purple-leaved variety of the common barberry and the form ex- 

 tensively used for low hedges {Berheris thunbergii). The former is a 

 spreader of the wheat rust and is legislated against in many States, 

 but the latter is immune. It is possible that a tall immune race 

 eventually may be produced from the cross between these two species. 



