I ought to have checked Bronson, but I don't have that part yet, unfortunately (and no time to get to the library). The additional verse you quote would be of Seeger's own making, presumably.

As I said earlier, the primary source was Caroline Cox. I had best be specific. First, then, the collated text, as published by Sharp in 1916:

The water is wide, I cannot get o'er
And neither have I wings to fly.
O go and get me some little boat
To carry o'er my true love and I.

A-down in the meadows the other day,
A-gath'ring flow'rs, both fine and gay,
A-gath'ring flowers, both red and blue,
I little thought what love could do.

I put my hand into one soft bush
Thinking the sweetest flow'r to find,
I prick'd my finger to the bone,
And left the sweetest flow'r alone.

I leaned my back up against some oak,
Thinking it was a trusty tree.
But first he bended and then he broke,
So did my love prove false to me.

Where love is planted, O there it grows,
It buds and blossoms like some rose;
It has a sweet and a pleasant smell,
No flow'r on earth can it excel.

Must I be bound, O and she go free!
Must I love one that does not love me!
Why should I act such a childish part,
And love a girl that will break my heart.

There is a ship sailing on the sea,
She's loaded deep as deep can be,
But not so deep as in love I am;
I care not if I sink or swim.

O love is handsome and love is fine,
And love is charming when it is true;
As it grows older it groweth colder
And fades away like the morning dew.

The Somerset versions from which the above was compiled are as follows:

1: from Mrs. Caroline Cox (70) at High Ham, Somerset, 8th August 1905.

Down in the meadows the other day,
Gathering flowers both fine and gay,
Gathering flowers both red and blue,
I little thought what love can do.

I put my hand into the bush
Thinking the sweetest flower to find,
I pricked my finger to the bone
And leaved the sweetest flower alone.

I leaned my back against some oak
Thinking it was a trusty tree.
First he bended, then he broke
And so did my false love to me.

There is a ship sailing on the sea
But it's loaded so deep as deep can be,
But not so deep as in love I am,
I care not whether I sink or swim.

Since my love's dead and gone to rest
I'll think on her who I love best.
I've sewed her up in flannel strong,
Have another now she's dead and gone.

2: from James Thomas (89) at Cannington, Somerset, 20th April 1906.

O down in the meadows the other day
A-gathering flowers both rich and gay,
A-gathering flowers both red and blue,
I little thought what love could do.

Where love is planted there do grow,
It buds and blossoms just like some rose,
For it has a sweet and a pleasant smell,
No flower on earth can it excel.

I fetched my back once against an oak,
I thought it had been some trusty tree,
For the first it bent and the next it broke,
So did my love prove false to me.

Must I go bound and she go free?
Must I love one that don't love me?
Why should I act such a childish part
To love a girl that will break my heart?

3: from Mrs. Elizabeth Mogg at Holford, Somerset, 30th August 1904.

The water is wide and I can't get over
Neither have I got wings to fly.
Go and get me O some little, little boat
For to carry over my true love and I.

Love is handsome, love is pretty,
Love is charming when it is true;
As it grows older it grows colder
And fades away like the morning dew.

I had two dogs under my father's table.
They do prick their ears when they do hear the horn.
When I'm dead, dear, it will be all over
And I hope my friends will bury me.

Maud Karpeles notes: "This song was noted from Mrs. Mogg again on 10th August 1906. On this occasion the following lines, which appear to have been taken from another song, replaced stanza 2".

In London city the girls are pretty,
Streets are paved with marble stones.
My true lover the clever a woman
As ever trod on English ground.

I'm often drunk but never sober,
I'm a rover in every degree.
When I'm drinking I'm always a-thinking
How to gain my love's company.