I do not remember Humboldt's fact about the heath regions.

Very curious the case of the broom; I can tell you something analogous on a small scale.

My father, when he built his house, sowed many broom-seeds on a wild bank, which did not come up, owing, as it was thought, to much earth having been thrown over them.
About thirty-five years afterwards, in cutting a terrace, all this earth was thrown up, and now the bank is one mass of broom.

I see we were in some degree talking to cross-purposes; when I said I did [not] much believe in hybridising to any extent, I did not mean at all to exclude crossing.

It has long been a hobby of mine to see in how many flowers such crossing is probable; it was, I believe, Knight's view, originally, that every plant must be occasionally crossed.