First-crosses made from this variety, each with a different form of P. sativum, are stated on the authority of Tschermak’s five cases, to follow exclusively the maternal seed-shape. From “schwach gerunzelte,” “feebly wrinkled,” Professor Weldon easily passes to “wrinkled,” and tells us that according as a round sativum or the Graue Riesen is used as mother, the first-cross seeds “will be round and smooth or flattened and wrinkled.”
As a matter of fact, however, the seeds of Graue Riesen though slightly wrinkled do not belong to the “wrinkled” class; but if the classification “wrinkled” and “round” is to be extended to such peas at all, they belong to the round. Mendel is careful to state that his round class are “either spherical or roundish, the depressions on the surface, when there are any, always slight”; while the “wrinkled” class are “irregularly angular, deeply wrinkled[96].”
On this description alone it would be very likely that Graue Riesen should fall into the round class, and as such it behaves in its crosses, being dominant over wrinkled (see Nos. 3 and 6, below). I can see that in this case Professor Weldon has been partly misled by expressions of Tschermak’s, but the facts of the second generation should have aroused suspicion. Neither author notices that as all five varieties crossed by Tschermak with Graue Riesen were round, the possibilities are not exhausted. Had Tschermak tried a really wrinkled sativum with Graue Riesen he would have seen this obvious explanation.
As some of my own few observations of first-crosses bear on this point I may quote them, imperfect though they are.
I grew the purple-flowered sugar-pea “Pois sans parchemin géant à très large cosse,” a soft-podded “mange-tout” pea, flowers and seed-coats coloured, from Vilmorin’s, probably identical with Graue Riesen.
1. One flower of this variety fertilised with Pois très nain de Bretagne (very small seed; yellow cotyledons; very round) gave seven seeds indistinguishable (in their coats) from those of the mother, save for a doubtful increase in purple pigmentation of coats.
2. Fertilised by Laxton’s Alpha (green; wrinkled; coats transparent), two flowers gave 11 seeds exactly as above, the purple being in this case clearly increased.
In the following the purple sugar-pea was father.
3. Laxton’s Alpha (green; wrinkled; coats transparent) fertilised by the purple sugar-pea gave one pod of four seeds with yellow cotyledons and round form.
4. Fillbasket (green; smooth but squared; coats green) fertilised by the purple sugar-pea gave one pod with six seeds, yellow cotyledons[97]; Fillbasket size and shape; but the normally green coat yellowed near the hilum by xenia.