294 Varietäten, Descendenz, Hybriden. 



one factor is concerned in determining the character of singleness. 

 Singleness is the dominant character. but gametogenesis is of 

 the peculiar type previously encountered in Matthiola , the factors 

 for singleness being distributed differently among the pollen grains 

 and the ovules. The pollen of the Singles is homogeneous as regards 

 the presence of some factor, which is essential for the manifestation 

 of singleness and is absent from some, at least, of the ovules With 

 regard to the ovules of the Singles and the pollen of the doubles, 

 the results are such as would occur if either (1) the ovules were 

 homogeneous and the pollen heterogeneous as regards the absence 

 of a factor determining singleness, or (2) the ovules were heteroge- 

 neous and the pollen homogeneous in respect of this factor. 



R. P. Gregory. 



Wheldale, Miss M., On the Formation ol Anthocyanin. 

 (Journ. Genetics, I. p. 132—158, 1911.) 



In this paper Miss Wheldale brings together the evidence bea- 

 ring on the problem of the chemical processes which are involved 

 in the formation of anthocyanin. As an outcome of this general 

 investigation she is able to bring forward an hypothesis which 

 affords an explanation, in terms of chemical reactions, of the pheno- 

 mena undertying the formation of soluble pigments. 



The author summarises her principal conclusions as follows: 

 "1. The soluble pigments of flowering plants, collectively termed 

 anthocyanin, are oxidation products of colourless chromogens of an 

 aromatic nature, which are present in the living tissues in combi- 

 nation with sugar as glucosides. 



2. The process of formation of the glucoside from chromogen 

 and sugar is of the nature of a reversible enzyme action. 



3. The chromogen can only be oxidised to anthoc3 r anin after 

 liberation from the glucoside and the process of oxidation is carried 

 out by one or more oxidising enzymes. 



4. The amount of free chromogen, and hence the quantity of 

 pigment formed at any time in a tissue, is inversely proportional to 

 the concentration of sugar and directly proportional to the concen- 

 tration of glucoside in that tissue. 



5. The local formation of anthocyanin which is characteristic of 

 the normal plant is due to local Variation in concentration of either 

 the free sugars or the glucosides in the tissues in which the pigment 

 appears. The abnormal formation of pigment under altered conditions 

 is dae to differences in the concentration of these same substances 

 due to changes in metabolism brought about by these conditions. 



6. On the above hypothesis the formation of anthocyanin is 

 brought into line with that of other pigments produced after the 

 death of the plant." 



The frequent appearance of pigment, under abnormal conditions. 

 in tissues which are normally unpigmented, justifies the supposition 

 that every part of the anthocyanic plant is provided with the mecha- 

 nism for the formation of pigment. 



The application of this hypothesis to the known facts of colour- 

 inheritance, expressed in terms of Mendelian factors is discussed. 

 The factor which prevents the formation of pigment, in races where 

 tbe coloured variety is recessive to the colourless type, has pre- 

 viously been regarded as representing a reductase or inhibitor On 

 the present hypothesis the appearance of colour might be explained 



