130 CARNEGIE INSTITUTION OF WASHINGTON. 



lay hold of the fundamental differences between the two sexes. He 

 concludes that the ''plus" races of mucors may be homologous in some 

 cases with what has been called male and in others with what has been 

 called female. 



INHERITANCE OF GERMINAL PECULIARITIES. 

 FLOWERING PLANTS. 



Portulaca. — In the breeding of this species Dr. Blakeslee has obtained 

 additional data as to the factors responsible for its color types. One 

 of the most interesting properties of the portulacas is their abihty to 

 undergo vegetative mutations. Dr. Blakeslee has a paper in press 

 describing the dominant vegetative mutations to normal habit of 

 growth that occur in recessive dwarfs, previously described in the Year 

 Book. Color characters also arise as dominant vegetative mutations. 

 Last year, in a line which for several generations had borne white 

 flow^ers and which had never shown red pigment in any of its parts, a 

 single plant was discovered one branch of which was slightly red and 

 bore white flowers with pink filaments. The two types of flowers were 

 selfed individually. Seeds from the normal white flowers have this 

 year given uniform pedigrees with white flowers, while seeds from the 

 flowers with pink stamens have given pedigrees with yellows and whites 

 in a 3:1 ratio. The pink-stamened white flov/ers therefore bred like 

 a heterozygous yellow. 



In another white-flowered pedigree, a plant was found which, in 

 addition to white flowers, bore some purple flowers and some flowers 

 the petals of which showed a centrally located "fan" of pale purple. 

 Seeds from the white flowers of this plant have bred like whites of this 

 line ; seeds from the purple flowers have segregated for purple and white, 

 while seeds from the "fans" have bred like the heterozygous purples. 



In a third line there have been found certain purple flowers breeding 

 like whites. The genetics of these three cases becomes intelligible, 

 Dr. Blakeslee concludes, if we consider them examples of periclinal 

 chimeras. Pigment in the petals is located almost exclusively in the 

 epidermal layers, while it is the subepidermal layers which take part in 

 the formation of the germinal tissue. In the first example, a white 

 epidermis covered a subepidermal tissue which carried factors for yel- 

 low. In the second example, in which the purple flowers and white 

 flowers with pale purple "fans" bred alike, the "fan" flowers had a 

 white epidermis with a subepidermal layer carrying the factors for pur- 

 ple, and therefore bred like a purple. In the third example, where a 

 purple flower bred like a white, the epidermal layer alone apparently 

 carried pigment and the subepidermal layers were devoid of factors for 

 purple pigmentation. The histological evidence so far obtained is in 

 accord with this conception. "Fan" flowers are devoid of purple in 

 the epidermis, but contain purple pigment in the cells sheathing the 

 bundles. Moreover, some purple flowers have been found with purple 



