13. GERANIACEAE.--Pelargonium zonale.
This plant, as a general rule, is strongly proterandrous, and is therefore adapted for cross-fertilisation by the aid of insects. (5/1. Mr. J. Denny, a great raiser of new varieties of pelargoniums, after stating that this species is proterandrous, adds 'The Florist and Pomologist' January 1872 page 11, "there are some varieties, especially those with petals of a pink colour, or which possess a weakly constitution, where the pistil expands as soon as or even before the pollen-bag bursts, and in which also the pistil is frequently short, so when it expands it is smothered as it were by the bursting anthers; these varieties are great seeders, each pip being fertilised by its own pollen. I would instance Christine as an example of this fact." We have here an interesting case of variability in an important functional point.) Some flowers on a common scarlet variety were self-fertilised, and other flowers were crossed with pollen from another plant; but no sooner had I done so, than I remembered that these plants had been propagated by cuttings from the same stock, and were therefore parts in a strict sense of the same individual. Nevertheless, having made the cross I resolved to save the seeds, which, after germinating on sand, were planted on the opposite sides of three pots. In one pot the quasi-crossed plant was very soon and ever afterwards taller and finer than the self-fertilised. In the two other pots the seedlings on both sides were for a time exactly equal; but when the self-fertilised plants were about 10 inches in height, they surpassed their antagonists by a little, and ever afterwards showed a more decided and increasing advantage; so that the self-fertilised plants, taken altogether, were somewhat superior to the quasi-crossed plants. In this case, as in that of the Origanum, if individuals which have been asexually propagated from the same stock, and which have been long subjected to the same conditions, are crossed, no advantage whatever is gained.
Several flowers on another plant of the same variety were fertilised with pollen from the younger flowers on the same plant, so as to avoid using the old and long-shed pollen from the same flower, as I thought that this latter might be less efficient than fresh pollen. Other flowers on the same plant were crossed with fresh pollen from a plant which, although closely similar, was known to have arisen as a distinct seedling. The self-fertilised seeds germinated rather before the others; but as soon as I got equal pairs they were planted on the opposite sides of four pots.
TABLE 5/49. Pelargonium zonale.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 22 3/8 : 25 5/8. Pot 1 : 19 6/8 : 12 4/8.
Pot 2 : 15 : 19 6/8. Pot 2 : 12 2/8 : 22 3/8.
Pot 3 : 30 5/8 : 19 4/8. Pot 3 : 18 4/8 : 7 4/8.
Pot 4 : 38 : 9 1/8.
Total : 156.50 : 116.38.
When the two lots of seedlings were between 4 and 5 inches in height they were equal, excepting in Pot 4, in which the crossed plant was much the tallest. When between 11 and 14 inches in height, they were measured to the tips of their uppermost leaves; the crossed averaged 13.46, and the self-fertilised 11.07 inches in height, or as 100 to 82. Five months later they were again measured in the same manner, and the results are given in Table 5/49.
The seven crossed plants now averaged 22.35, and the seven self-fertilised 16.62 inches in height, or as 100 to 74. But from the great inequality of the several plants, the result is less trustworthy than in most other cases. In Pot 2 the two self-fertilised plants always had an advantage, except whilst quite young over the two crossed plants.
As I wished to ascertain how these plants would behave during a second growth, they were cut down close to the ground whilst growing freely. The crossed plants now showed their superiority in another way, for only one out of the seven was killed by the operation, whilst three of the self-fertilised plants never recovered.