There are about twenty species, but the number cannot be very accurately defined - several, usually regarded as distinct, being probably merely variable forms of the same type, and the ease with which the trees intercross has led to the appearance of many hybrids. [Please select]
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PALLAS, on the influence of domestication upon the sterility of intercrossed species. [Please select]
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PALLAS, on the influence of domestication upon the sterility of intercrossed species, i. [Please select]
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--PEAS: AMOUNT OF DIFFERENCE IN THE SEVERAL KINDS, CHIEFLY IN THE PODS AND SEED--SOME VARIETIES CONSTANT, SOME HIGHLY VARIABLE--DO NOT INTERCROSS. [Please select]
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, the fact of their perfect, or even increased, fertility when intercrossed in the most complicated manner becomes a strong argument in favour of their having all descended from a single species. [Please select]
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On the other hand, some cultivated plants rarely or never intercross, for instance, the common pea and sweet-pea (Lathyrus odoratus); yet their flowers are certainly adapted for cross fertilisation. [Please select]
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