This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
In accordance with the recommendations of the Nomenclature Commission of the Botanical Club of the American Association for the Advancement of Science, specific or varietal names derived from persons, or used as the genitive of generic names or as substantives, are printed with the initial capital letter. There is much difference of opinion as to the desirability of this practice, many botanists, and almost all zoologists, following the principle of writing all specific names with a small initial letter. Should this custom prevail, much information concerning the history and significance of the specific names would be lost. Thus in the Tulip-tree, Liriodendron Tulipifera, the specific name Tulipifera was the ancient generic name; and the same with Lythrum Salicaria, L. Hyssopifolia, L. Vul-neraria, and many other species. In all other forms of writing, personal adjectives such as Nuttallii, Engelmanni or Torreyi are printed with capitals. We adhere to the ordinary literary usage.