5. Express (“blue”-green cotyledons and transparent skins; round) fertilised with purple sugar-pea gave one pod with four seeds, yellow cotyledons, shape round, much as in Fillbasket.
6. British Queen (yellow cotyledons, wrinkled, white coats) ♀ × purple sugar-pea gave two pods with seven seeds, cotyledons yellow, coats tinged greenish (xenia?), all round.
So much for the “Purple” sugar-pea.
I got similar results with Mange-tout Debarbieux. This is a soft-podded Mange-tout or sugar-pea, with white flowers, large, flattish, smooth seeds, scarcely dimpled; yellow cotyledons.
7. Debarbieux fertilised by Serpette nain blanc (yellow cotyledons; wrinkled; white skin; dwarf) gave one pod with six seeds, size and shape of Debarbieux, with slight dimpling.
8. Debarbieux by nain de Bretagne (very small; yellow cotyledons; very round) gave three pods, 12 seeds, all yellow cotyledons, of which two pods had eight seeds identical in shape with Debarbieux, while the third had four seeds like Debarbieux but more dimpled. The reciprocal cross gave two seeds exactly like nain de Bretagne.
But it may be objected that the shape of this large grey pea is very peculiar[98]; and that it maintains its type remarkably when fertilised by many distinct varieties though its pollen effects little or no change in them; for, so long as round varieties of sativum are used as mothers, this is true as we have seen. But when once it is understood that in Graue Riesen there is no question of wrinkling, seeing that the variety behaves as a round variety, the shape and especially the size of the seed must be treated as a maternal property.
Why the distinction between the shape of Graue Riesen and that of ordinary round peas should be a matter of maternal physiology we do not know. The question is one for the botanical chemist. But there is evidently very considerable regularity, the seeds borne by the cross-breds exhibiting the form of the “grey” pea, which is then a dominant character as much as the seed-coat characters are. And that is what Tschermak’s Graue Riesen crosses actually did, thereby exhibiting dominance in a very clear form. To interject these cases as a mystery without pointing out how easily they can be reconciled with the “law of dominance” may throw an unskilled reader into gratuitous doubt.
Finally, since the wrinkled peas, Laxton’s Alpha and British Queen, pollinated by a large flat mange-tout, witness Nos. 3 and 6 above, became round in both cases where this experiment was made, we here merely see the usual dominance of the non-wrinkled character; though of course if a round-seeded mother be used there can be no departure from the maternal shape, as far as roundness is concerned.
Correns’ observations on the shapes of a “grey” pea crossed with a round shelling pea, also quoted by Professor Weldon as showing no dominance of roundness, are of course of the same nature as those just discussed.