The stem bark is also a frequent seat of the active principle, of which the outer portion contains the greater amount, according to the valuable experiments of Howard.
Some plants owe their therapeutic importance to their wood, others to their leaves or flowers, and regarding the localization of the active principle in these parts we have nothing especial to indicate. The fruit, however, may have a pericarp consisting of mucilage, starch, sugar and gum, etc., while the seeds contain fatty matter, fixed or essential oils or alkaloids, as is the case with coffee and cacao. In view of these facts, we repeat that it is indispensable to use that part of each plant which I have indicated as applicable to a determined case or condition.
I earnestly hope that the physicians and pharmacists practising in the Philippines may undertake investigations and experiments regarding the therapeutic properties of the plants of my native land, and that my endeavors may have acted as a stimulus or inspiration to the loyal and earnest study of the subjects that are now awakening such interest, not only in Europe and America, but in India and Japan.
I should be pleased to receive notes, plants or reports of researches from any one interested in the subject matter of this book, and I shall consider it a pleasure, as well as a duty, to devote my forces, small as they may be, to aiding any one who may do me the honor to claim my assistance.
T.H.P De Tavera
Paris, April, 1892.