If our botanical professors would come forth into the true light of nature, they should accept the position of pupil to her, and not assert that of teacher. So long as they continue to peep and botanize upon her grave, or over ancient mounds and Hadrianic tumuli, they will never find out the cunning of her processes, much less the means she employs to accomplish her perfected ends. This modern idolatry of "hypotheses," with our chronic neglect of what nature _does_, is the great scientific stumbling-block of the age in which we live. Our botanists all agree that certain plants and trees disappear--hopelessly die out--from the _absence_ of "necessary conditions;" when will they come to recognize the reverse of this undeniable proposition, and agree that the _presence_ of necessary conditions may cause the same plants and trees to make their appearance, that is, spring into life in obedience to some great primal law, as unerringly obeyed by nature as the attractive force of the universe itself? For nearly half a century the fact has been known that the geographical distribution of the European flora, and especially that of the British Islands, was referable to latitude, elevation, and climatic conditions. As early as 1835, Mr. Hewett Watson, a well-known botanist of that day, in his published "Remarks on the Geographical Distribution of Plants, in connection with Latitude, Elevation, and Climate," drew the attention of the botanical world to this remarkable feature of plant distribution; while the late Professor Edward Forbes pursued the same line of thought in his attempt to show how geographical changes had affected plant areas in Great Britain as far back as the last glacial drift. And yet all our botanical writers have been steadily persisting on immense plant-migrations to account for their geographical distribution, and have given us maps without number to show how the vegetal hosts have traversed vast continents, swam multitudinous seas, braved the fiery equator, and scaled the summits of the loftiest Andes. In the mean time, no botanist of any distinguished note, except M. De Candolle, has confidently ventured to question this migration theory, so imposing and formidable has been the array of names which have frowned down, like so many gigantic ghauts, upon the audacious questioner.