However, in the very sentence preceding the one thus quoted, Matthew admits that it's a collateral issue put in only to spice up an otherwise insipid book on planting and timber. Here's the full passage (Matthew 1831, v-vi):
"It may be thought presumptuous in a person who has never had the curiosity to peruse the British classic authors on planting and timber—Evelyn, Hanbury, Marshall, Miller, Pontey—to make experiment of the public sufferance. The author does not, however, think any apology necessary; as, if the public lose time unprofitably over his pages, he considers the blame attachable to them, not to him. A writer does not obtrude as a speaker does, but merely places his thoughts within reach.
As the subject [planting and timber], notwithstanding its great importance, might, per se, be felt dry and insipid by the general reader, accustomed to the luxuries of modern literature, the author has not scrupled to mix with it such collateral matter as he thought might serve to correct the aridity. The very great interest of the question regarding species, variety, habit, has perhaps led him a little too wide."