A contribution to our knowledge of seedlings / by the Right Hon. Sir John Lubbock.

  • Lubbock John, Sir, 1834-1913.
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: A contribution to our knowledge of seedlings / by the Right Hon. Sir John Lubbock. 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.

    19/1278
    subject of various important memoirs, which, however, have been almost exclusively descriptive. Dalmer ^ indeed quotes Schleiden, who, speaking of Berberis, pointed out that among the normal anatropous ovules here and there one occurs which is orthotropous, and that these never develop into seeds (' Die Befruchtung der Ovule scheint mir aber in ganz bestimmter Beziehung zu dem vorgeschriebenen Lauf der PoUenschlauche zu stehen, denn stets beobachtete ich, dass diese regelwidrige atropen Eichen unbefruchtet blieben'). The pollen-tubes, however, would naturally follow the regular course ; and we could not, I think, deduce a general conclusion from such rare and abnormal cases. Dalmer himself does not seem to have done so; for, after referring to the different forms of ovules, he observes that ' sometimes the form of the ovule appears to be adapted so as to facilitate the entrance of the pollen-tube' (' scheint zuweilen die Gestalt des Ovulums dem Eintritt des PoUenschlauches angepasst zu sein '). Even here, then, the explanation I venture to suggest seems referred to rather as an exceptional occurrence than as a general explanation of this remarkable arrangement. It must be admitted that there are some cases in which the anatropy of the ovule appears at first sight rather disadvantageous than otherwise. Most of these can, I believe, be explained, while in some it is possible that the plants retain, even perhaps to their present disad- vantage, an arrangement inherited from an ancestral condition in which it was beneficial. I hope, however, to enter into this question more fully on a future occasion. The mature seed contains the more or less differentiated embryo, in some cases, as in Larkspur {Delphinium) (fig. 104), very small, consisting only of a small basal portion the radicle', which on germination gives rise to the primary root, and one (Monocotyledons), two (Dicotyledons), or several (Conifers) seed-leaves or cotyledons, sheathing a microscopic plumule— from which the future stem is developed. The rest of the space is occupied by the mealy, oily, fleshy, or horny endo- sperm. In other cases, as in the Ash (Fraxinus) (fig. 46) or Castor on (Ricinus) (fig. 52), the embryo is much larger, and ZciL.Tsto'p^'Is?'*^ PoUensohliiuche bei den Angiospermen,' Jenaisch