Dear Sir—

Referring to your Letter of the 29^th. March last,¹ which I regret I have been unable fully to reply to earlier—I find it is somewhat difficult to give a direct answer to your enquiry respecting the duration of crossed varieties of Peas, as that are several influences at work which appear to militate against, or at least to vary or interfere with the duration, in different varieties, the results of crossing— In the first place I hold that the natural tendency of all the cultivated peas, is to run, or to assume a climbing & tall growing habit; and that the dwarf varieties are all either the result of continued selection or crossing in that direction, and therefore all varieties raised by crossing a normally vigorous & tall variety with a dwarf sort as ‘Tom Thumb’ or ‘Little Gem’ (each 1 foot high) or with a semi-dwarf as ‘Ringleader’ (2$\frac{1}{2}$ feet) and which are less vigorous than their more vigorous parent have a tendency to revert to the height & vigour of that parent—² There appears also to be, in the first-early varieties which do not normally exceed 2$\frac{1}{2}$ feet in height & are less productive than later sorts, a tendency, when grown in quantity, to become later, more vigorous & more productive— slender growing sorts like the true ‘Ringleader’, if left unselected for a few generations, would assume the conditions of the somewhat more vigorous & more fertile ‘Sangster’s N^o 1 & ‘Early Emperor’ which are usually a few days later than Ringleader   I think this may arise through harvesting, for when early peas are grown in quantity for seed, they are usually pulled or cut, not when the earliest are ripe, but rather when the medium or average, & often not until the latest are fit, and sometimes, from unseasonable weather they are left on the ground when a considerable proportion of the earliest will have shelled out, others are taken by birds, mice & various enemies, and so, after frequent repetitions the later ripening & more vigorous of the produce materially predominate— when also early peas are grown in gardens similar causes are at work, for the earliest are generally gathered green for consumption & the tail, containing the latest, is often saved for seed— this repeated year after year, combined with the lower scale of productiveness of the early sorts, leads to the produce, at the end of a few generations, becoming more, instead of less, vigorous or rather to the gradual disappearance of the weaker & the ultimate predominance of the stronger— This is practically remedied or met by selection, and from this source about every decade a new first early pea turns up which is announced as at least a week earlier than all others, although in respect to earliness, we are still about where we were 200 years ago—

Doubtless some of these causes, at least with the less vigorous sorts, go to neutralize or counterbalance any natural tendency to reduced vigour which may exist—

My answer therefore to your enquiries must be restricted to the duration of those varieties only which are raised from crossing tall and normally vigorous sorts, and, as regards these, actual experience will not carry me beyond some 12 generations, for although I commenced crossing the pea about 20 years ago, I have not grown ‘Prolific Longpod’ the first variety I raised every successive year from seed of the previous year, but often when it was 2 or 3 years old—³ this variety was produced from a cross between ‘Prizetaker’ (4 f^t. 6 in high) & ‘Sangster’s N^o1’ (3 f^t. 6 in) and I have never perceived in it any diminution of vigour, but what might have arisen from external causes, such as thicker seeding & diminished attention to cultivation, which is sure to follow in a few years after the introduction of a new & expensive variety when it becomes more plentiful & the novelty has subsided—

Subject to these qualifying and exceptional causes & circumstances & the ordinary laws of reversion, I believe, that after the varieties have become fixed (ie. when the great tendency to reversion has subsided, which is usually about the 4^th. or 5^th generation, all my crossed peas have retained their pristine vigour, and in confirmation of this view, I have seen, from time to time fine & vigorous samples with the haulm of several of them grown under ordinary field culture, & notably last autumn, one of ‘Prolific Longpod’ which was quite as vigorous as I ever grew or have seen it—and I have never been able to gather any satisfactory evidence, beyond what may be explained by external causes, of diminished vigour in any of the cultivated varieties of Peas—

I shall be glad to render you any further information or assistance in my power & regretting the delay which I hope has not inconvenienced you—

I am Dear Sir, | your’s faithfully | Thomas Laxton

Cha^s Darwin Esq | Down | Beckenham | Kent