From many of the facts above stated, it may be inferred that the chemical compounds of plants do not occur at random.  Each stage of growth and development has its own particular chemistry.

It is said that many of the constituents found in plants are the result of destructive metabolism, and are of no further use in the plant’s economy.  This subject is by no means settled, and even should we be forced to accept that ground, it is a significant fact that certain cells, tissues, or organs peculiar to a plant secrete or excrete chemical compounds peculiar to them, which are to be found in one family, or in species closely allied to it.

It is a fact that the chemical compounds are there, no matter why or whence they came.  They will serve our purposes of study and classification.

The result of experiment shows that the presence of certain compounds is essential to the vigor and development of all plants and particular compounds to the development of certain plants.  Plant chemistry and morphology are related.  Future investigations will demonstrate this relation.

In general terms, we may say that amides and carbohydrates are utilized in the manufacture of proteids.  Organic acids cause a turgescence of cells.  Glucosides may be a form of reserve food material.

Resins and waxes may serve only as protection to the surfaces of plants; coloring matters, as screens to shut off or admit certain of the sun’s rays; but we are still far from penetrating the mystery of life.

A simple plant does what animals more highly endowed cannot do.  From simplest substances they manufacture the most complex.  We owe our existence to plants, as they do theirs to the air and soil.

The elements carbon, oxygen, hydrogen, and nitrogen pass through a cycle of changes from simple inorganic substances to the complex compounds of the living cell.  Upon the decomposition of these bodies the elements return to their original state.  During this transition those properties of protoplasm which were mentioned at the beginning, in turn, follow their path.  From germination to death this course appears like a crescent, the other half of the circle closed from view.  Where chemistry begins and ends it is difficult to say.—­Jour.  Fr. Inst.

  [Footnote 1:  A lecture delivered before the Franklin Institute,
  January 24, 1887.]

  [Footnote 2:  Studien uber das Protoplasm, 1881.]

  [Footnote 3:  Vines, p. 1.  Rostafinski:  Mem. de la Soc. des Sc. 
  Nat. de Cherbourg, 1875.  Strasburger:  Zeitschr., xii, 1878.]

  [Footnote 4:  Botany:  Prantl and Vines.  London, 1886, p. 110.]

  [Footnote 5:  For the literature of starch, see p. 115, Die
  Pflanzenstoffe, von Hilger and Husemann.]

[Footnote 6:  Kutzing:  Arch.  Pharm., xli, 38.  Kraus and Millardet:  Bul.  Soc.  Sciences Nat., Strasbourg, 1868, 22.  Sorby:  Jour.  Lin.  Soc., xv, 34.  J. Reinke:  Jahrb.  Wissenscht.  Botan., x, B. 399.  Phipson:  Phar.  Jour.  Trans., clxii, 479.]

  [Footnote 7:  Prantl and Vines, p. 111.]