Mr. Rushworth, however, though not usually a great talker, had still more to say on the subject next his heart. “Smith has not much above a hundred acres altogether in his grounds, which is little enough, and makes it more surprising that the place can have been so improved. Now, at Sotherton we have a good seven hundred, without reckoning the water meadows; so that I think, if so much could be done at Compton, we need not despair. There have been two or three fine old trees cut down, that grew too near the house, and it opens the prospect amazingly, which makes me think that Repton, or anybody of that sort, would certainly have the avenue at Sotherton down: the avenue that leads from the west front to the top of the hill, you know,” turning to Miss Bertram particularly as he spoke. But Miss Bertram thought it most becoming to reply—

“The avenue! Oh! I do not recollect it. I really know very little of Sotherton.”

Fanny, who was sitting on the other side of Edmund, exactly opposite Miss Crawford, and who had been attentively listening, now looked at him, and said in a low voice—

“Cut down an avenue! What a pity! Does it not make you think of Cowper? ‘Ye fallen avenues, once more I mourn your fate unmerited.’”

He smiled as he answered, “I am afraid the avenue stands a bad chance, Fanny.”
Chapter 6.

Hmm.......these lines, that Fanny quotes ,are by the poet William Cowper.

They way in which Edmund immediately recognises her reference seem to indicate a shared admiration for the poet.We know that edmund had directed her real education,so must assume that Edmund recommended Fanny read the poets works:

but his attentions were otherwise of the highest importance in assisting the improvement of her mind, and extending its pleasures. He knew her to be clever, to have a quick apprehension as well as good sense, and a fondness for reading, which, properly directed, must be an education in itself. Miss Lee taught her French, and heard her read the daily portion of history; but he recommended the books which charmed her leisure hours, he encouraged her taste, and corrected her judgment: he made reading useful by talking to her of what she read, and heightened its attraction by judicious praise. In return for such services she loved him better than anybody in the world except William: her heart was divided between the two.

The lines that fanny quoted are taken from his epic poem The Task. Here is a link to the poem in full ;-) I cant help but think Lady Betram's sofa is a sly reference by JA to the poems opening line ;-)

I sing the Sofa....

Back to more serious topics.....;-)

The Task was poem much admired by the Abolitionist movement for its anti slavery stance. And yes, Thomas Clarkson sings its, and the poet Cowper's praises for his abhorrence of slavery as expressed in this poem in Book II,The Time Piece :

The last of the necessary forerunners and coadjutors of this class, whom I am to mention, was our much-admired poet, Cowper; and a great coadjutor he was, when we consider what value was put upon his sentiments, and the extraordinary circulation of his works. There are few persons, who have not been properly impressed by the following lines:

“My ear is pain’d,
My soul is sick with every day’s report
Of wrong and outrage with which earth is fill’d.
There is no flesh in man’s obdurate heart,
It does not feel for man. The nat’ral bond
Of brotherhood is sever’d as the flax
That falls asunder at the touch of fire.
He finds his fellow guilty of a skin
Not colour’d like his own, and having pow’r
T’ inforce the wrong, for such a worthy cause
Dooms and devotes him as his lawful prey.
Lands intersected by a narrow frith
Abhor each other. Mountains interpos’d,
Make enemies of nations, who had else,
Like kindred drops, been mingled into one.
Thus man devotes his brother, and destroys;
And, worse than all, and most to be deplor’d
As human Nature’s broadest, foulest blot,—
Chains him, and tasks him, and exacts his sweat
With stripes, that mercy with a bleeding heart
Weeps, when she sees inflicted on a beast.
Then what is man? And what man, seeing this,
And having human feelings, does not blush
And hang his head to think himself a man?
I would not have a slave to till my ground,
To carry me, to fan me while I sleep,
And tremble when I wake, for all the wealth
That sinews bought and sold have ever earn’d.
No: dear as freedom is,—and in my heart’s
Just estimation priz’d above all price,—
I had much rather be myself the slave,
And wear the bonds, than fasten them on him.
We have no Slaves at home—then why abroad?
And they themselves once ferried o’er the wave
That parts us, are emancipate and loos’d.
Slaves cannot breathe in England; if their lungs
Receive our air, that moment they are free;
They touch our country, and their shackles fall .
That’s noble, and bespeaks a nation proud
And jealous of the blessing. Spread it then,
And let it circulate through every vein
Of all your empire—that where Britain’s pow’r
Is felt, mankind may feel her mercy too.”
Thomas Clarkson, The History of the Abolition of the African Slave-Trade, vol. 1 [1808],Chapter 111

and also, in this passage he details the very active part Cowper played in furthering the work of the Abolitionist movement:

The amiable poet Cowper had frequently made the Slave-trade the subject of his contemplation. He had already severely condemned it in his valuable poem The Task. But now he had written three little fugitive pieces upon it. Of these the most impressive was that, which he called "The Negro’s Complaint", and of which the following is a copy:

“Forced from home and all its pleasures,
Afric’s coast I left forlorn,
To increase a stranger’s treasures,
O’er the raging billows borne;
Men from England bought and sold me,
Paid my price in paltry gold;
But, though theirs they have inroll’d me,
Minds are never to be sold.
“Still in thought as free as ever,
What are England’s rights, I ask,
Me from my delights to sever,
Me to torture, me to task?
Fleecy locks and black complexion
Cannot forfeit Nature’s claim;
Skins may differ, but affection
Dwells in black and white the same.
“Why did all-creating Nature
Make the plant, for which we toil?
Sighs must fan it, tears must water,
Sweat of ours must dress the soil.
Think, ye masters, iron-hearted,
Lolling at your jovial boards,
Think, how many backs have smarted
For the sweets your cane affords.
“Is there, as you sometimes tell us,
Is there one, who rules on high;
Has he bid you buy and sell us,
Speaking from his throne, the sky?
Ask him, if your knotted scourges,
Fetters, blood-extorting screws,
Are the rueans, which duty urges
Agents of his will to use?
“Hark! he answers. Wild tornadoes,
Strewing yonder sea with wrecks,
Wasting towns, plantations, meadows,
Are the voice with which he speaks.
He, foreseeing what vexations
Afric’s sons should undergo,
Fix’d their tyrants’ habitations
Where his whirlwinds answer—No.
“By our blood in Afric wasted,
Ere our neeks received the chain;
By the miseries, which we tasted
Crossing, in your barks, the main;
By our sufferings, since you brought us
To the man-degrading mart,
All sustain’d by patience, taught us
Only by a broken heart:
“Deem our nation brotes no longer
Till some reason you shall find
Worthier of regard, and stronger,
Than the colour of our kind.
Slaves of gold! whose sordid dealings
Tarnish all your boasted powers,
Prove that you have human feelings,
Ere you proudly question ours.”

This little piece, Cowper presented in manuscript to some of his friends in London; and these, conceiving it to contain a powerful appeal in behalf of the injured Africans, joined in printing it. Having ordered it on the finest hot-pressed paper, and folded it up in a small and neat form, they gave it the printed title of “A Subject for Conversation at the Tea-table.” After this, they sent many thousand copies of it in franks into the country. From one it spread to another, till it travelled almost over the whole island. Falling at length into the hands of the musician, it was set to music; and it then found its way into the streets, both of the metropolis and of the country, where it was sung as a ballad; and where it gave a plain account of the subject, with an appropriate feeling, to those who heard it.
As above, Volume 2 chapter 1.

JA knew and loved Cowper's poems. She even planned her garden at Southampton with him in mind:

Our garden is putting in order by a man who bears a remarkably good character, has a very fine complexion, and asks something less than the first. The shrubs which border the gravel walk, he says, are only sweetbriar and roses, and the latter of an indifferent sort; we mean to get a few of a better kind, therefore, and at my own particular desire he procures us some syringas. I could not do without a syringa, for the sake of Cowper's line. We talk also of a laburnum. The border under the terrace wall is clearing away to receive currants and gooseberry bushes, and a spot is found very proper for raspberries.
Letter to Cassandra,February 8th 1807

I can't help but think that she agreed with his abolitionist standpoint. And I think her inclusion of him in MP is very deliberate. Two of her most sympathetic characters in the book are fans.......

Another of her adored writers also quoted these lines from Cowper : William Gilpin in his Observations on the Western Parts of England etc.:

Farnham consists chiefly of one. long, thorough-fare street, and is principally remarkable for its being the summer-residence of the Bishop of Winchefter.

Farnham-castle stands high, and was formerly a fortress of confiderable reputation. It was built by a Bishop of Winchester in the time of King Stephen, when castles were much in fashion, and made some figure in the troubled reign of that prince.

It afterwards figured in the times of Lewis the Dauphin, in the insurrections of the barons, and in the civil wars of the laft century. During these last troubles it was blown up by Sir William Wailer; though not with that picturesque judgment with which many castles in those times were demolished. Very little is left that can make a pleasing picture. After the restoration it deposited its military character, and was changed again into an Episcopal palace by Bishop Morley; but it has ever since been neglected. The present bishop is the first who has paid any attention, for many generations, to Farnham-castle. He has greatly improved the house, and has fitted it up in such a manner, as will probably make it an object to every future bishop.

The keep, or inner castle, is left standing in its ruins, and is still a curious piece of antiquity. It is surrounded by a deep ditch, which, together with the area of the castle, containing about two acres, makes an excellent kitchen garden.

Behind the house extends a park, about four miles in circumference, which the bishop found as much neglected and out of order as the house itself. It was cut with unlicensed paths, the trees were mangled to browze the deer, and a cricket ground had so long been suffered, that the people conceived they had now a right to it. This last was a great nuisance. Such a scene of riot and disorder, with stands for selling liquor, juft under the castle windows, could not easily be endured. The bishop took the gentlest methods he could to remove the nuisance; and at length, though not without some difficulty, got it effected.

Having thus removed nuisances from his park he began to embellish it. He improved the surface, he laid out handsome roads and walks, he planted young trees, and prote&ed the old trees from farther ill usage.

Across the park runs an avenue a mile long of ancient elms. The bishop could not persuade himself to remove this monument of antiquity; and I think with great judgment hath left it in its old form; for though an avenue is neither a pleasing nor a picturesque arrangement of trees, yet the grandeur of this gives it confequence; and its connection with the antiquity of the castle gives it harmony. Here the poet, after mourning the lois of other avenues, may exult:

Ye fallen avenues! once more I mourn
Your fate unmerited: once more rejoice
That yet a remnant of your race furvives.

About a quarter of a mile from the house arises in the park an eminence, on which stands a keeper's lodge. The situation is conspicuous, but the object unpleasing . A few acres, therefore, around it are inclosed, a green-houfe is built to skreen the lodge, and walks are cut, and adorned with different kinds of curious shrubs in high perfection.

From this eminence are feveral openings into the country, particularly one towards Moor-Park, where that enlightened genius, Sir William Temple, (retiring in disgust from state affairs, when Charles II's politics received a tincture from France,) cultivated every part of literature with an elegance of taste uncommon at that day. His heart lies buried, according to his will, in a flyer urn, under a dial in his garden. A singularity of this kind, in preferring a garden to a church-yard, rather favours the opinion which Bishop Burnet gives us, of Temple's religious sentiments.

In moot of the views from the park at Farnham-castle, Crooksbury-hill is a distinguished feature; which, tradition says, Sir William Temple always considered as of the greatest ornaments of his place. This shews his love for nature; though in laying out his grounds, the awkward idea of the times misled both his theory and practice.
pages 38-41.

JA knew of Farnham Castle- and made a joke about it in one of her early letters.

I think both these references by Clarkson and Gilpin are why JA made her reference to the poem The Task in MP.

And as to Moor Park apricots... I think it is no coincidence that she made Dr Grant and Mrs Norris argue about the provenance of the "Moor park " apricot at the rectory: Gilpin mentioned the house where it was developed in the passage quoted above:

This image of the fuzz-free apricot was created by William Hooker in1818

The Moor Park Apricot had been developed by Lord Anson at his home, Moor Park. Which , of course, as referred to by Gilpin in the passage quoted above and one with which I think a person declared to be " enamoured of Gilpin on the Picturesque " would have been familiar ;-)