Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

The Evolutionary Status of Plant Families in Relation to some Chemical Properties

James B. McNair
American Journal of Botany
Vol. 21, No. 8 (Oct., 1934), pp. 427-452
Stable URL: http://www.jstor.org/stable/2436185
Page Count: 26
  • Read Online (Free)
  • Download ($12.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Evolutionary Status of Plant Families in Relation to some Chemical Properties
Preview not available

Abstract

The object of this paper is to show that, when the plant families which contain fats, volatile oils, and alkaloids are first separated according to the climate of habitat, some chemical and physical properties of these substances vary in accordance with the degree of evolution of the plant families containing them; and the probability is that, the more highly organized the plant, the more complex are its chemical products. The fact that climatic changes in physical and chemical properties from glycerides, volatile oils, and alkaloids are consistent causes one to deduce that a sufficient number of chemical analyses of the determinant substances have been made from sufficiently representative ranges of evenly dispersed families and that any additional analyses will fall in the groups already established and will only more, strongly confirm the conclusion already determined. In any one climate any physical or chemical changes in specific chemical products may perhaps serve as an index of the degree in evolution of the plant family in which these changes took place. It is necessary that the chemical substances used for this purpose be as specific as the plant unit used, be it family, genus, or species. Glycerides, volatile oils, and alkaloids are defined and shown to have certain chemical properties often specific for species. Some constituents of volatile oils have already been used to show morphological evolution in the genera of Eucalyptus and Callitris. Alkaloids have been used in the genus Aconitum. Tropical alkaloids may be arranged in a scatter diagram with the average molecular weights and the botanical position of the containing plant families as coordinates. When this is done, the straight-line trend produced indicates that the higher the plant family in evolutionary progression the more likely it is to produce alkaloids of high molecular weight. Likewise it is shown that alkaloids which are formed by more than one family when first separated as to climate assume positions in the evolutionary scale proportional to their average molecular weights. Similarly, tropical glycerides may be arranged in a scatter diagram in which the average iodine numbers and the botanical positions of the producing plant families are used as coordinates. When this is done the straight-line trend produced indicates that the higher the plant family in evolutionary position the more likely it is to form glycerides with large iodine numbers (and low melting points). In the case of tropical volatile oils scatter diagrams may be made with their specific gravities as one coordinate and the botanical positions of the producing plant families as the other coordinate. The resulting trend is upward in accordance with the increase in specific gravity and the increase in plant evolution. Another scatter diagram for tropical volatile oils may be made in which one coordinate is the refractive index and the other is the producing family's evolutionary position. The trend of this arrangement is down and coincides with the results obtained from the use of the specific gravity, for a low index in refraction carries with it a concomitant increase in specific gravity. It can therefore be concluded that the volatile oils of the families highest in evolutionary development have constituents with a large number of double bonds (low saturation), more aromatic compounds, or more sulfur and nitrogen compounds with small amounts of substances of low molecular weight or small quantities of terpenes or bodies of the fatty series. The heat of combustion of the acids contained in the tropical volatile oils increases with the increase in the average systematic position of the families producing them. This coincides with the findings obtained from the study of the specific gravity and refractive index of volatile oils. The heats of combustion of the alcohols which are constituents of the tropical volatile oils increase with the increase in the average systematic position of the families producing them. This result likewise agrees with and confirms the findings obtained from the study of the specific gravities and refractive indices of volatile oils. All of these results demonstrate what may be a general rule for the tropics and perhaps for all climates-that the more highly organized the plant the more highly organized are likely to be its chemical products.

Page Thumbnails

  • Thumbnail: Page 
427
    427
  • Thumbnail: Page 
428
    428
  • Thumbnail: Page 
429
    429
  • Thumbnail: Page 
430
    430
  • Thumbnail: Page 
431
    431
  • Thumbnail: Page 
432
    432
  • Thumbnail: Page 
433
    433
  • Thumbnail: Page 
434
    434
  • Thumbnail: Page 
435
    435
  • Thumbnail: Page 
436
    436
  • Thumbnail: Page 
437
    437
  • Thumbnail: Page 
438
    438
  • Thumbnail: Page 
439
    439
  • Thumbnail: Page 
440
    440
  • Thumbnail: Page 
441
    441
  • Thumbnail: Page 
442
    442
  • Thumbnail: Page 
443
    443
  • Thumbnail: Page 
444
    444
  • Thumbnail: Page 
445
    445
  • Thumbnail: Page 
446
    446
  • Thumbnail: Page 
447
    447
  • Thumbnail: Page 
448
    448
  • Thumbnail: Page 
449
    449
  • Thumbnail: Page 
450
    450
  • Thumbnail: Page 
451
    451
  • Thumbnail: Page 
452
    452