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A hybrid between P. ayacahuite and P. wallichiana, described in 1933 from trees growing at Westonbirt, Glos., and named after Sir George Holford, the owner from 1892 until his death in 1926. They had been raised in 1904 from the famous specimen of P. ayacahuite var. veitchii in the arboretum, pollinated by a tree of P. wallichiana growing nearby. The shoots differ from those of P. wallichiana in usually being hairy, and the cones are broader than in that species. From P. ayacahuite it differs, at least in the type, by the apices of the cone-scales not being reflexed, but A. F. Mitchell has found that second-generation hybrids, of which many have been raised and distributed, often incline strongly to P. ayacahuite, but can usually be identified by the orange-brown bark, the greater vigour and the more open crown.
There are several specimens at Westonbirt of the original first-generation hybrids, planted in 1906, ranging from 70 to 92 ft in height and 51⁄2 to 7 ft in girth (1974). Some others, of the first or second generation, are: Wakehurst Place, Sussex, in West Wood, 79 × 7 ft (1970); Borde Hill, Sussex, pl. 1931, 62 × 91⁄4 ft (1974); R.H.S. Pinetum, Wisley, 60 × 91⁄4 ft (1969); Lythe Hill, Haslemere, Surrey, 60 × 8 ft (1969).
specimens: Westonbirt, Glos., two original trees in Holford Ride, both 98 × 63⁄4 ft (1983) and another in Broad Drive, 72 × 71⁄4 ft (1982); Wakehurst Place, Sussex, 92 × 73⁄4 ft (1984); Borde Hill, Sussex, pl. 1929, 75 × 101⁄4 ft (1981); Tilgate Park, Sussex, 75 × 71⁄4 ft (1982); R.H.S. Garden, Wisley, Surrey, Pinetum, 72 × 101⁄2 ft (1983); Lythe Hill, Haslemere, Surrey, 85 × 81⁄2 ft (1977).
Another hybrid from the pollen of P. wallichiana, the seed-parent in this case being P. strobus, the Weymouth pine. It was described in 1930 from a tree found growing on the estate of Fritz Graf von Schwerin near Berlin, which had been planted in 1905 as P. strobus. It resembles P. wallichiana in habit and in some foliage characters, but the cones recall those of P. strobus. The same cross was made artificially at the Forest Research Station, Alice Holt. One tree from the cross has grown 10 ft in three years (Mitchell, Conifers in the British Isles, p. 242).
From the Supplement:
P. × schwerinii – The tree at the Forest Research Station, Alice Holt, Hampshire, pl. 1957, measures 56 × 41⁄4 ft (1983).