Thoreau, in the following quote, is talking about flowers, and as you may know, most flowers that are hybridized in order to gain a more beautiful flower, lose their ability to pollenate and propagation is left to making a cutting; a much harsher and singular process. Now in the case of the tulip shaped rose, whose beauty we all admire, they have not only lost their ability to be pollenated but have lost their fragrance as well. In the following quote he is drawing a lesson for us, and I have to admit I'm having difficulty understanding it clearly. If a principal just pops out at you, please share it.
"Simplicity is the law of nature for men as well as for flowers. When the tapestry (corolla) of the nuptial bed (calyx) is excessive, luxuriant, it is unproductive.... Such a flower has no true progeny, and can only be reproduced by the humble mode of cuttings from its stem or roots ----- The fertile flowers are single, not double." Thoreau.