Accueil Recherche simple par mot (textes et titres)
Textes en anglaisLyell, Charles, Principles of Geology (extract of Vol. 2)
Navigation dans le document
|<  << Page : 53 >> >|
shed pollen, and then laying on foreign pollen upon the stigma. The same 
experiment has since been repeated, with success, by Wiegmann, who found that he 
could bring back the hybrids to the exact likeness of either parent, by crossing 
them a sufficient number of times.

The blending of the characters of the parent stocks, in many other of Weigmann's 
experiments, was complete ; the colour and shape of the leaves and flowers, and 
even the scent, being intermediate, as in the offspring of the two species of 
verbascum. An intermarriage, also, between the common onion and the leek (Allium 
cepa and A. porrum) gave a mule plant, which, in the character of its leaves and 
flowers, approached most nearly to the garden onion, but had the elongated 
bulbous root and smell of the leek.

The same botanist remarks, that vegetable hybrids, when not strictly 
intermediate, more frequently approach the female than the male parent species, 
but they never exhibit characters foreign to both. A re-cross with one of the 
original stocks, generally causes the mule plant to revert towards that stock ; 
but this is not always the case, the offspring sometimes continuing to exhibit 
the character of a full hybrid.

In general, the success attending the production and perpetuity of hybrids among 
plants, depends, as in the animal kingdom, on the degree of proximity between 
the species intermarried. If their organization be very remote, impregnation 
never takes place ; if somewhat less distant, seeds are formed, but always 
imperfect and steril. The next degree of relationship yields hybrid seedlings, 
but these are barren ; and it is only when the parent species are very nearly 
allied, that the hybrid race may be perpetuated for several generations. Even in 
this case the best authenticated examples seem confined to the crossing of 
hybrids with individuals of pure breed. In none of the experiments most 
accurately detailed does it appear that both the parents were mules.

Wiegmann diversified, as much as possible, his mode of bringing about these 
irregular unions among plants. He often 
Créer son extrait avec MonPDF Marquer cette page avec votre compte ICEberg+

Auteur et directeur de publication : Pietro CORSI,
Hébergement : Centre de Calcul de l'IN2P3-CNRS.