WHIlfc FINES IN EASTERN NORTH AMERICA 2 11 



(Wright, 1958), P. sil in - Is a taller tree than P. oetnbra, with shuiici 

 leaves and larger cones (Rehder, 1949). Both species are suitable as 

 ornamentals where a slow-growing tree of dense habit is desired (Fig. oB 

 and Wyman, 1965) . 



P. PARVIFLORA SIEB. AND ZUCC. 



Japanese white pine is slow-growing in North America and usually ha: 

 a poor form for timber (Fig. 6C and D, and Wright, 1958). The northern 

 variety pentaphylla is a straighter form that might have some possi- 

 bilities for breeding (Fig. 6C) . A 40-year-old specimen at Rochester, 

 New York, apparently of the pentaphylla variety, was 15 m tall and 38 cm 

 in diameter at age 40. The species is susceptible to the white pine 

 weevil and therefore has little promise as a forest tree for most of the 

 Northeast (Wright and Gabriel, 1959). 



P. PUMILA RE GEL 



The Japanese stone pine, P. pumi-la, is considered by recent invest] 

 gators to be more closely allied to P. parvi flora than to the P. oembra- 

 P. sibi-rica group (Ferre*, 1960; Malyshev, 1960). It is a shrubby form of 

 no timber value, though Heimburger (unpublished notes) believes that it 

 may be of breeding value because of resistance to sulfur dioxide injury. 



HYBRIDS OF P. STROBUS AND EUROPEAN AND ASIATIC SPECIES 



In addition to natural hybrids, many different white pine hybrids 

 have been obtained by artificial crossing (Righter and Duffield, 1951; 

 Riker and Patton, 1954; Heimburger, 1958; Wright, 1959). These hybrids 

 have been tested in most parts of the United States and southern Canada 

 (Southeastern Forest Experiment Station, 195D; Righter and Duffield, 

 1951; Wright, 1959; Fowler, unpublished data; Kriebel and Fowler, 1965). 

 Botanical descriptions have been prepared for many of them (Keng and 

 Little, 1961; Little and Righter, 1965), though some of the descriptions 

 do not fully agree with observations of specimens from different parents 

 or of the same biotypes growing in different localities. Apparently 

 parental genotype and test environment can affect both morphological and 

 physiological responses of white pine hybrids (Kriebel and Fowler, 1965) . 



Some of the hybrids can outgrow either parent, at least in the early 

 years. An example is P. montioola x strobus in the Northeast (Wright, 

 1959) and the Northwest (Bingham, Squillace and Patton, 1956). However, 

 records of hybrid vigor in the Northwest are based on nursery growth. 

 Later performance in the field has varied. In Idaho, P. montioola x 

 strobus hybrids were taller than P. montioola trees with the same female 

 parents 10 years after outplanting. But in western Montana, snow damage 

 was severe to hybrid progenies as well as to progenies of both P. 

 montioola and P. strobus (Barnes and Bingham, 1962; R. J. Steinhoff, 

 personal oommunioation) . 



Other combinations with early hybrid vigor are P. griffithii x 

 strobus, P. strobus x griffithii, P. flexilis x griffithii, P. montioola 

 x griffithii, P. ayaoahuite x griffithii, P. ayaoahuite x strobus, and 

 P. strobus x ayaoahuite (Wright , 1959). P. strobus x griffithii is more 

 vigorous than P. strobus in northern Ohio and more winter-hardy than P. 

 griffithii (Kriebel, 1963). 



