A. D. Darbishire. 
the red, blue and violet. The simultaneous presence of the two 
colouring matters in the unripe Pea may be demonstrated in the 
following way. Some unripe Peas are steeped in alcohol; a green 
extract is thus produced ; but it only remains green if it is 
kept in the dark. If it is exposed to daylight or even to gaslight, it 
fades to yellow. And a spectroscopic examination of this yellow 
liquid shows that it contains the same pigment as the extract of 
ripe yellow Peas. 
Both yellow and green Peas therefore start with both chloro¬ 
phyll and xanthophyll; and the difference between them is that in 
the yellow the chlorophyll fades during ripening. The green 
chloroplasts in yellow Peas gradually lose their pigment, as the 
seeds ripen, and when it has disappeared altogether they are left in 
the cell as pale yellow globules. This is as far as the facts go. 
The hypothesis which these facts seem to warrant is that the pair 
of factors to which the colours of the cotyledons of Pisum are due 
are not “yellow” and “green” but some factor which effects 
the fading of the chlorophyll during ripening, and the absence of 
this factor; of which the former, which results in the production of 
a yellow Pea, is dominant, whilst the latter is recessive. 
Cotyledon Shape. 
The application of this hypothesis to the pair of characters 
pertaining to the shape of the cotyledons seems destined to throw 
much light on the fundamental nature of the two factors involved, 
although the form in which, on the analogy of the foregoing case, 
it first presented itself seemed unreal and preposterous. For, on 
this analogy, we should have to conceive of the pair as con¬ 
sisting of the factor for roundness and the absence of this 
factor on a background of wrinkledness But we shall see that, 
the two characters, round and wrinkled, can be shewn to be due to 
the presence and absence, respectively, of a particular factor. 
Some clue as to the probable nature of this factor was afforded by 
the attempt to elucidate the causes to which the wrinkling of 
wrinkled seeds is due. All Peas, whether round or wrinkled when 
ripe, are round when unripe ; they also, of course, contain much 
more water than the dry ones. It is, therefore, not unnatural to 
suspect that the wrinkling of the wrinkled Pea may be due to the 
fact that, starting with a mass similar to that of the unripe round 
Pea, it loses more water during the ripening process than the round 
one does. It is not convenient to measure this ; but the same end 
