In Romeo and Juliet, what is Friar Lawrence's special area of knowledge?

The answer to this question can be found in Act II scene 3
of this excellent tragedy, which is of course the first time we are introduced to Friar
Lawrence in the play. His introductory speech, before Romeo enters, makes it clear his
expert knowledge of the world of plants, herbs and flowers and their usage. Note what he
says in these lines:

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O, mickle is the powerful grace that
lies

In plants, herbs, stones, and their true
qualities;

For naught so vile that on the earth doth
live

But to the earth some special good doth
give;

Nor aught so good but,strained from that fair
use,

Revolts from true birth, stumbling on
abuse.

In these lines Friar
Lawrence thus indicates the power that lies in knowing the "true qualities" of plants
and herbs. He says that everything on earth has some importance or special quality.
Friar Lawrence's skill and knowledge lies in knowing the "true quality" of such herbs
and plants and how to use them to help man. This knowledge of course becomes critical
for the plot of the play when he gives Juliet a potion that will put her in a death-like
state but without killing her.