United States or Turkmenistan ? Vote for the TOP Country of the Week !
In some instances this analogy goes still further, and incompletely pinnate leaves are produced with two or more pairs of leaflets. Besides this variable type another has been described by Willdenow.
The difference is so striking and affords such a reliable feature that Koch proposed to make two distinct varieties of them, calling the pure type Fraxinus excelsior monophylla, and the varying trees F. excelsior exheterophylla. Some writers, and among them Willdenow, have preferred to separate the "one-leaved" forms from the species, and to call them Fraxinus simplicifolia.
Hence it may be assumed that the "one-leaved" ashes have sprung suddenly but frequently from the original pinnate species. The pure type of Willdenow should, in this case, be considered as due to a slightly different mutation, perhaps as a pure retrograde variety, while the varying strains may only be eversporting forms. This would likewise explain part of their observed inconstancy.
Word Of The Day