radical, radicle

Radical or radical means extreme; very different from the ordinary, usual, or existing--
These changes seem to radical; maybe we could do this one step at a time.
They have made some radical alterations to the original plans.

Radical may also mean a a person who holds or advocates very different views; who advocates extensive or profound change in a political or social system--
He was quite a radical in college, but he's toned down his rhetoric since then.
He likes to think of himself as a radical, but he's barely liberal, in reality.

Radical may also mean a group of atoms behaving as a unit--
Harmful chemicals can produce a free radical, capable of damaging cells.

Radical is also a mathematical term or sign, meaning the root of a number, the square root if no other number is before it--
√4=2 ( The square root of four equals two. )

Radicle or radicle ( rhymes with radical ) means the part of a plant embryo that develops into the root--
When a seed germinates, the radicle grows down, into the soil.
The radicle is the first part of a seedling to grow.

Radicle may also mean one of the smallest parts of a vein or nerve--
The smallest radicle of any nerve might be irritated by the toxin.

Now that you know that, you can say--
"He has a radical new theory about the effect of electricity on the radicle of a seed."