298 Oxydases and Pigments of Plants 



oxydase. It happens very frequently that the walls of these cells take 

 on also a brown stain. Although this staining of the wall may be 

 due to diffusion of the oxidized benzidine derivative from the cell, yet 

 the possibility is not precluded that in the living plant oxydase may 

 occur in the walls of the cells. We are not in a position to make a 

 positive statement on this subject but may point out that changes, often 

 of a remarkable nature, go on in cell walls and in some cases, for 

 example, in the macrospores of species of Selaginella very considerable 

 changes of structure and dimensions occur in cell walls which are far 

 removed from contact with cytoplasm. Therefore it would seem not 

 unreasonable to suppose that oxydases may play a part in the growth 

 processes of cell walls, and that the occurrence of wall staining after 

 the treatment of a tissue with an oxydase reagent may be due to the 

 formation in situ of the colour substance indicative of oxydase and not 

 to the passage of that substance from the cytoplasm to the wall. 



F. Dominant White Varieties. 



We have now to consider the oxydase content of those varieties of 

 P. sinensis known to students of Genetics as Dominant Whites. As 

 the term implies, Dominant Whites present the appearance of albinism 

 but, as it also suggests, the albino-like appearance masks a distinct and 

 remarkable genetical constitution. Hitherto the only test serving to 

 discriminate between Recessive and Dominant Whites has been the 

 breeding test. Recessive Whites crossed with coloured varieties give a 

 coloured F^ generation ; Dominant Whites when mated with similar 

 coloured varieties yield a white F^ generation. The F^ plants from the 

 cross, recessive white x colour, give on self-fertilization or on inter- 

 breeding an F„ consisting of 3 coloured : 1 white. The F^ generation 

 derived from self-fertilized or inter-bred F-^ plants from a cross between 

 coloured and dominant white consists of 3 white : 1 coloured. The 

 phenomenon of dominant whiteness does not appear to be very common 

 among plants. It is exemplified by the flowers of Primula sinensis 

 (Bateson, 1906), and the Foxglove (Digitalis purpureus, Keeble, 

 1910 b). Among animals a similar phenomenon occurs with respect to 

 coat colour in certain breeds of fowls, for example White Leghorns 

 (Bateson, 1906). The interpretation which meets the facts of the 

 genetical behaviour of Dominant Whites is well known and involves 

 the existence of a factor which, even though the factor or factors for 

 colour be present, prevents the development of pigment. In other 



