Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.

Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    primitive form, to a less extent between different species and genera. The result of these relationships is seen on the one hand in the fact that with plants which live socially only the most vigorous seedlings arrive at full maturity, while the weaker ones are smothered, as may be seen in any young plantation; on the other hand, that species and genera which differ greatly from one another can thrive side by side, because their requirements are different and the competition between them is less. From the fact that plants whose organisation differs can thrive better side by side on the same soil in consequence of the diminished competition between them, Darwin drew the important and pregnant conclusion that in the propagation of the varieties of one primitive form those new forms must be the best able to maintain themselves in the wild state which differ most from the primitive form and from one another, while the intermediate forms are gradually dispossessed. This is the reason why the connecting forms between the different species of a genus are so often want- ing, although the conclusion cannot be avoided that the species arose by variation from a single ancestral form, and by the propagation of varieties. In its larger features (but on that account more conspicuously) the struggle for ex- istence between the various forms of plants, the competition for space, food, and light, are manifested in the luxuriant growth of what we term weeds in our gardens and fields. Our cultivated plants are able to bear our climate, and the soil supplies what they require for their vigorous growth. But a number of wild plants are still better adapted to the climate ; and they grow still more vigorously, rapidly, and luxuriantly on cultivated soil, and their seeds or rhizomes are everywhere present in enormous quantities. If the cultivated plants are not carefully protected from the weeds, the latter soon dis- possess them of the ground which was set apart for them. Every country and every soil has its own peculiar weeds; i. e. under any particular external conditions there are always certain forms of plants which thrive best and drive out the cultivated plants. To a certain extent we have a measure of the amount of advantage which weeds have over cultivated plants in the amount of labour bestowed by man on their destruction in order to preserve and maintain his nurselings. The primitive forms of our cultivated plants are mostly natives of other countries, where they are not only sufficiently adapted for the climate, but are able to sustain competition with their neighbours. The number of species or of individuals of any species which we find in a meadow, a marsh, &c. is not a matter of chance ; it does not depend merely on the number of seeds of one or another species produced or brought to the locality ; every one of these species would, if it alone existed there or were protected by cultivation, of itself cover the space of ground in a short time; and yet there is a definite relationship between the numbers of individuals of the different species when left to themselves, a relationship which de- pends on the specific power of each particular species to maintain itself in the struggle with the rest1. How complicated may be this relationship in the cases of only two nearly related forms of plants in their struggle for existence in particular localities, has been described as exhaustively as clearly by Nageli in the case of various Alpine plants. ‘The interne- cine war,’ he says2 3, ‘ is obviously most severe between the species and races that are most nearly related, because they require the same conditions of existence. Achillea 1 [How the relationship subsisting between the species in permanent pastures may be disturbed by the application of different manures, may be seen in Lawes and Gilbert’s paper on this subject in Joum. Roy. Agric. Soc. vol. XXIV, 1863.—Ed.] 2 Sitzungsber. der kon. bayer. Akad. der Wiss. Dec. 15,1865.