[Enclosure]

Brentwood, Essex.

May 19. 1872

Dear Sir Charles.

My father⁵ is obliged to you for the offer of a specimen of Unio littoralis from Grays and will be glad of it as an authentic example. He thinks that you should in your next edition of either “Elements” or “Principles” mention that you obtained the shell yourself at Grays as there does not seem to be any reliable personal statement extant of anyone having found the shell there and as it seems to be absent from the recent excavations in which the Cyrena in association with Unio pictoria occurs in myriads doubts would arise hereafter which such a statement by you may obviate⁶

It occurs to me that you may care to know my own experiments as to the state of things alluded to in your second Vol of the Principles bottom of page 306 & top of p 307—⁷ in 1859 (13 years ago) I planted a number of the pips of 3 varieties of apple. 1 was the Stone pippin 2 The Norfolk Biffin & 3 an eating apple which our gardener called a Cockle pippin   The offspring of 1 & 2 were robust plants. & I preserved some of them without grafting & they are now trees 12 to 15 feet high. Only one of these ungrafted progeny bore fruit and that was for one year only (about 1863 or 4). the rest never have borne fruit & I should judge by their appearance never will do so but so far as their leaves afford a criterion they are true apples of the same stock as their progenitors   they are however evidently barren, not producing even flowers save occasionally a blossom here & there which never comes to anything. The one tree which bore had only 3 apples on it & they were all 3 of them true stone pippins not distinguishable in any way from the parent apple. This tree never bore or blossomed again until this spring when it has now a few blossoms on it. Those individuals of the crop thus sprung from pips which I grafted or budded bore in 1863 & have done ever since. None of these ungrafted trees bear any greater resemblance to the wild crab than do the original fruit bearing trees from which they sprung & D^r. Hooker is quite right in saying that the wild crab is a different thing. But is not I think quite accurate in stating that the pips of apples produce “crabstates” of the varieties to which they belong.⁸ My experience & what I can learn from cottagers who have tried to raise trees from pips is that the apple produces true scions in its progeny but that most of these are barren or nearly so the rare exceptions which do occur of prolific individuals forming the new varieties from time to time introduced   The apple seems therefore to me to afford a striking example of the reason why some of our cultivated forms of the vegetable kingdom cannot become permanent wild species viz that they cannot reproduce themselves in sufficient force & number to compete in the battle of life. It is quite otherwise with the varieties of Brassica, for these are extremely fertile & so long as they are not allowed to intermingle produce a perpetual succession of the varietal form but as all the varieties freely intermingle with each other they when allowed to run wild become represented by the most reproductive variety among them & this is a sort of kale of which a few specimens (called rogues by gardeners) generally shew themselves in all sowings of every one of the cultivated varieties & are carefully eliminated by the gardener from the rest— The apple & the cabbage are thus it seems to me restrained from becoming wild species by precisely opposite agencies the one by feebleness of reproductive power & the other by the excessive reproductive power of one of its varieties— The wild crab is on the contrary extremely fertile—we have an old one here in a hedge that is covered every year with flowers & fruit—& the leaves are quite different from the apple progeny. The pips of no 3 produced very feeble plants & these died away in a year or two & their leaves were so entirely unlike apple or crab leaves that the late D^r Woodward⁹ who saw them in 1860 would not believe that they had sprung from apple pips   The leaves were trifid like those of the hawthorn & as apples and pears are sometimes grafted on the hawthorn, (I have some pears here which bear freely grafted by myself on simple hawthorns & others on a hawthorn hedge) I have wondered whether the Cockle pippin from which these feeble examples spring might not have been growing on a hawthorn stock & become so far affected by the hawthorn stock as to have shewn it in their pips progeny— I in the same year planted a number of peach & nectarine stones the progeny of which grew into good sized trees but were never healthy, always dying back in their branches— Our garden peaches are always budded on to plum stocks owing I suppose to this unhealthy constitution of the seedling peach. Some of them bore fruit sparingly but the fruit would never come to maturity invariably dropping off that of some of the trees at an early stage of growth & that of others at a more advanced but still immature stage. It is clear therefore that none of those could reproduce themselves as wild species for a similar reason to that which restrains the apple from becoming wild but I was told by a New Zealand colonist that the peach tree has sprung up along the river valleys of that island abundantly from stones thrown away (derived from garden peaches introduced) & that these wild peaches bear an abundance of fruit equal to the finest garden peaches of Europe.¹⁰ (I fancy that something similar occurs in America). It would then appear that the climatal conditions of a Pacific island remote from the parent Country of the wild almond from which the peach is supposed to have sprung are favorable enough to convert a garden fruit that cannot under the conditions of an European climate become wild into a true wild species.¹¹

Many years ago I tried the seed of red geraniums of choice varieties & I found these produced for the most part barren progeny or at least geraniums with very few blossoms & those very poor.

I could also say much about what I consider to be the popular delusion of birds restraining the development of insect life having watched that problem many years but I have already I doubt exhausted your patience as well as my paper.

I am Dear Sir Charles | yours faithfully | Searles V. Wood Jn