4. To the _difference in the form of the ripe pods_. These are either simply inflated, never contracted in places; or they are deeply constricted between the seeds and more or less wrinkled (_P. saccharatum_). 5. To the _difference in the colour of the unripe pods_. They are either light to dark green, or vividly yellow, in which colouring the stalks, leaf-veins, and calyx participate[26]. [26] One species possesses a beautifully brownish-red coloured pod, which when ripening turns to violet and blue. Trials with this character were only begun last year. [Of these further experiments it seems no account was published. Correns has since worked with such a variety.] 6. To the _difference in the position of the flowers_. They are either axial, that is, distributed along the main stem; or they are terminal, that is, bunched at the top of the stem and arranged almost in a false umbel; in this case the upper part of the stem is more or less widened in section (_P. umbellatum_)[27]. [27] [This is often called the Mummy Pea. It shows slight fasciation. The form I know has white standard and salmon-red wings.] 7. To the _difference in the length of the stem_. The length of the stem[28] is very various in some forms; it is, however, a constant character for each, in so far that healthy plants, grown in the same soil, are only subject to unimportant variations in this character. [28] [In my account of these experiments (_R.H.S. Journal_, vol. XXV. p. 54) I misunderstood this paragraph and took “axis” to mean the _floral_ axis, instead of the main axis of the plant. The unit of measurement, being indicated in the original by a dash (′), I carelessly took to have been an _inch_, but the translation here given is evidently correct.] In experiments with this character, in order to be able to discriminate with certainty, the long axis of 6–7 ft. was always crossed with the short one of 3/4 ft. to 1-1/2 ft. Each two of the differentiating characters enumerated above were united by cross-fertilisation. There were made for the 1st trial 60 fertilisations on 15 plants. 2nd " 58 " " 10 " 3rd " 35 " " 10 " 4th " 40 " " 10 " 5th " 23 " " 5 " 6th " 34 " " 10 " 7th " 37 " " 10 " From a larger number of plants of the same variety only the most vigorous were chosen for fertilisation. Weakly plants always afford uncertain results, because even in the first generation of hybrids, and still more so in the subsequent ones, many of the offspring either entirely fail to flower or only form a few and inferior seeds. Furthermore, in all the experiments reciprocal crossings were effected in such a way that each of the two varieties which in one set of fertilisations served as seed-bearers in the other set were used as pollen plants.