W. F. R. Weldon 
237 
side in the same pod. An excellent coloured figure of one of these pods is given 
(loc. cit. Plate 9, Fig. 1), and is the only figure I have found which illustrates segre- 
gation of colours in hybrid Peas of the second generation. In 1849 Gartner 
(No. 12, pp. 81 — 8.5) described the result of crossing races of Peas; the yellow- 
seeded Pariser Wachserbse which he calls Pisum sativum luteum, was fertilised 
(a) with pollen of P. sativum macrospermum which had seeds of an impure greenish- 
yellow, and {h) with pollen of the green-seeded P. sativum viride. In the first 
case the hybrid seeds were all pure yellow ; in the second case twelve seeds were 
produced in four hybrid pods ; and these were all of a greenish-yellow colour, 
although the greenish tinge disappeared from some of them on drying. Another 
yellow-seeded Pea (P. sativum nanum rej>ens) fertilised with the pollen of the 
green-seeded P. sativum viride gave five hybrid pods with seeds, of which one 
contained five dirty green seeds, a second had five seeds which were " not dis- 
tinctly yellow, but yellowish green," although they lost their greenness after being 
dried for two months. The others were not yellow like the mother, but "dirty 
yellow." It is clear that the " greenness " of P. sativum viride did in these cases 
affect the colour of the seeds, when its pollen was used to fertilise plants of yellow- 
seeded race, though it is difficult to judge exactly how great the effect was. The 
disappearance of the green colour on drying m;iy have been simply due to the 
development of an air-space between the seed-coat and the cotyledons, which as 
Tschermak (No. 27) has pointed out may obscure the colour of the cotyledons in 
the dry seed, or it may have been due to a real increase in yellowness. The 
flowers of P. sativum viride were fertilised with pollen from two pure yellow- 
seeded races (P. sativum luteum and P. sativum nanum repens), and in the first 
case the seeds produced were " not distinctly yellow, still less blue or green, but 
dirty yellow." In the second case the seeds produced were yellow ; and when 
P. sativum viride was fertilised by P. sativiim macrospermum the seeds produced 
were apparently yellower than those of the male parent. 
The effect of the dominance of yellowness over greenness of cotyledons in 
hybrids of the first generation, if it were indeed universal, would be so striking 
that one can hardly conceive that the great founders of our modern races of Peas, 
such as Knight (No. 18) and Laxton (No. 19), should have failed to notice it, and 
yet neither of them, in describing experience gained from crossing great numbers 
of plants, says that it is of general occurrence. 
The colour of seeds of the first hybrid generation has not, so far as I can 
discover, been carefully described between the time of Mendel and the year 1893, 
when Giltay (No. 14), who does not appear to have known Mendel's work, crossed 
several yellow-seeded peas with the green-seeded race Reading Giant, and 
found that the colour of the cotyledons was always yellow, showing tliat Mendel's 
law of dominance was completely valid in this case. (Giltay points out the 
necessity of removing the seed-coats before determining the colour of the 
cotyledons; this is also emphasised by Tschermak, and I have found it quite 
necessary even in seeds of pure race.) In 1900 general attention was directed to 
