Gallesio makes the same statement with
respect to oranges. I have myself known extensive crossing to occur with
the common rhubarb. For Leptosiphon, Verlot 'Des Varieties' 1865 page
20. I have not included in my list the Carnation, Nemophila, or
Antirrhinum, the varieties of which are known to cross freely, because
these plants are not always self-fertile. I know nothing about the
self-fertility of Trollius Lecoq 'De la Fecondation' 1862 page 93,
Mahonia, and Crinum, in which genera the species intercross largely.
With respect to Mahonia it is now scarcely possible to procure in this
country pure specimens of M. aquifolium or repens; and the various
species of Crinum sent by Herbert 'Amaryllidaceae' page 32, to Calcutta,
crossed there so freely that pure seed could not be saved.) Much other
indirect evidence could be given with respect to the extent to which
varieties of the same species spontaneously intercross.
Gardeners who raise seed for sale are compelled by dearly bought
experience to take extraordinary precautions against intercrossing. Thus
Messrs. Sharp "have land engaged in the growth of seed in no less than
eight parishes." The mere fact of a vast number of plants belonging to
the same variety growing together is a considerable protection, as the
chances are strong in favour of plants of the same variety
intercrossing; and it is in chief part owing to this circumstance, that
certain villages have become famous for pure seed of particular
varieties.
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