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
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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![enveloping the grains, is the primitive form ; if it is not, then no plant is now known which can be considered as the ancestral form of our numerous and extremely diverse varieties of maize. In this case also continued cultivation has increased the amount of difference between the different varieties, as well as to a prodigious extent that between them and the primitive form ; and the separate varieties are distinguished from one another by a number of different characters. Some are only feet high, others as much as 15 to 18 feet; the grains stand on the rachis in rows varying from six to twenty in number; they may be white, yellow, red, orange, violet, streaked with black, blue, or copper-red ; their weight varies sevenfold ; their form also varies extremely; there are varieties with three kinds of fruit of different form and colour on one rachis; and a great number of other differences also occur1. These instances may suffice to show to what an extent the amount of deviation of the varieties of a primitive form may increase under cultivation2. It is much more difficult, and to a great extent impossible, to prove directly to what extent the variation of wild forms can increase without cultivation, because historical evidence is in this case generally impossible, or can only be obtained indi- rectly or conjecturallv. But since the laws of variation are unquestionably the same in the case of wild as of cultivated plants—although they operate in the two cases under different conditions—we may for the time at least assume as probable that plants vary as greatly in the wild as in the cultivated state. We shall however in the sequel have to examine a number of weighty considerations which lead to the con- clusion that variation has produced infinitely greater effects in originating the various wild forms of plants than those which we perceive in cultivated varieties3. The variation of cultivated plants shows that there is only one cause for the internal and for the external hereditary resemblance between different plants, and that this cause is the common origin of similar forms from one and the same ancestral form. When we meet with corresponding phenomena in wild forms, and when we find that with them as with cultivated plants dissimilar forms are connected by a series of intermediate forms, just as we find to be the case between the primitive forms of cultivated plants and their most abnormal varieties, we are forced to the conclusion that in wild plants also a similar affinity is the only cause of resemblance. The extraordinarily numerous forms, for example, of the widely distributed genus Hieracium present phenomena similar in many respects to those of cultivated gourds, cabbages, &c. In addition to a number of forms which are considered to be species, there are a still greater number of intermediate forms, some of which only are hybrids, the greater part perfectly fertile varieties. Niigeli *, who has made this genus 1 See Darwin l. c. vol. I, p.365, and Metzger /. c. p.207. No great value with reference to variation and the constancy of varieties must be set on the result of experiments on cultivated plants, since the possibility of hybridisation was not excluded. Some varieties of maize appear to hybridise with difficulty. 2 Further material will be found collected in Darwin’s and Metzger’s works already quoted, and in De Candolle, Geographie botanique ; Paris, 1855. 3 [H. Hoffmann gives in the Bot. Zeit. for April 27 and May 1, 1874, an account of an inter- esting series of experiments on the extent to which the characters which distinguish the allied species Papaver Rhceas and dubium and Phaseolus vulgaris and muUijlorus can be made to vary by cultivation, and on the tendency of the cultivated varieties to revert to the parent-form.—Ed.] * Sitzungsberichte der kon. bayer. Akad. derWiss. March 10, 1866.](https://iiif.wellcomecollection.org/image/b21981437_0844.jp2/full/800%2C/0/default.jpg)
