[Enclosure]

On a mode of producing Varieties by Pruning.

About eight years since I commenced two experiments one on red wheat & the other on white for the purpose of producing a six-set variety, i.e. six grains in a spikelet, three or four being the usual number in cornfields.⁶ Before the plants flowered all the stems were cut away except one & as soon as the ear was protruded the upper half was cut off, & all the fresh shoots at the base of the stems were removed about once a week or fortnight till the ears were ripened.

The result was that the six-set was produced & in the third year a seven-set spikelet, which as far as I know has not been observed by agriculturists & it seemed very probable that eight-set could be produced.

The experiment which had only economical purposes in view was then discontinued because it was found that cutting off the upper half of the ear for only three years had the very singular effect of occasioning the upper half of the ear in the red wheat to be nearly barren & shrivelled, & of converting the upper half of that in the white into an unnaturally dense spike approaching that of Phalaris Canariensis;⁷ it was in this that the seven-set was produced. Would not this account for varieties with short spikes? A plant growing in barren ground would have unusually short spikes which in time might perhaps become a permanent variety.

One suggestion may be interesting. If the central bud of a Sun-flower were cut off when the plant was about a foot high, & those of the lateral branches which sprouted afterwards when they became a few inches long & the plant was then left to flower, I quite expect that a corymbous⁸ variety of the Sun-flower would be produced having many small heads in the place of one, which could be propagated by seed, & the corymbs increased in density by continuing the pruning.

This leads to the inference that progressive development depends in great measure on the condition of the parents at the time of fertilization;— whatever that condition may be it is unalterably stamped on the offspring. But it appears to me that this is not the only cause of progressive development. Spontaneous generation although it has been regarded as unphilosophical is nevertheless it appears to me rendered most probable by Dactylium oogenum,⁹ & if so it is in all probability a very common occurrence. This being the case, spontaneous alteration at the time of generation, not depending on the condition of the parents, would perhaps be a phenomenon not so unlikely to occur as otherwise might be supposed. The production of a nectarine on a peach tree I regard as an instance of this spontaneous alteration,¹⁰ & at Hampstead there is an Elm tree one arm of which has an apparently different leaf, I think considerably smaller, & much denser branches than the rest of the tree, which I suppose to arise from one of the buds having spontaneously a new mode of growth.¹¹

If then buds at the time of generation can take on a new mode of growth, of course embryos can do the same, & here we should have a prolific source of new varieties.

I therefore attribute progressive development to two causes which act either separately, or, not improbably, sometimes in conjunction.