1925] REHDER, AMELASORBUS, A NEW BIGENERIC HYBRID 155 



plura basi foliolis 2-4 ellipticis vel elliptico-oblongis 2-3 cm. longis dentatis 

 instructa, supra basin plus minusve lobata lobis apicem versus decrescenti- 

 bus, supra medium indivisa, ceterum ut in foliis ramulorum floriferorum; 

 petioli 1.5-3 cm. longi; stipulae lineari-lanceolatae, circiter 5 mm. longae, 

 caducae. Inflorescentia paniculata ad 5 cm. longa, tenuiter villosula; 

 axes secundarii racemosi, 1-3 inferiores foliis suffulti, infimus 5-9-florus 

 pedicello infimo interdum 2-floro, apicem versus decrescentes ; pedicelli 

 2-3 mm., in fructu ad 6 mm. longi; hypanthium extus et sepala triangulari- 

 ovata acuminulata utrinque villosula; petala alba, oblonga, 9-10 mm. 

 longa, obtusa, ad basin cuneatam supra lanata, apice sparse lanato-ciliosa; 

 stamina 20, longiora 3 mm. longa, antheris ut videtur sterilibus; styli 5, 

 raro 4, 2.5-3 mm. longi, staminibus paullo breviora, ad medium ovarii 

 liberi basi villosi, hypostylio medio fere ad basin villoso; ovarium apice 

 dense villosum, 4-5-loculare, loculis in parietie exteriore manifeste costata 

 costa post anthesin in lamellam crassam ad medium loculum prominentem 

 accrescente, ideo fructus imperfecte 8-10-loculatus. Fructus subglobosus 

 vel globoso-ovoidea, 6-8 mm. diam., in sicco atro-coerulea, pruinosa, in 

 vivo (sec. collectorem) rubra, coeruleo-pruinosa, sepalis persistentibus 

 erect is ovato-lanceolatis circiter 4 mm. longis coronatus; semina pauca 

 perfect a, ellipsoidea, compressa, circiter 4 mm. longa, castanea. 



Idaho: summit of Elk Butte, Clearwater County, alt. about 2000 m., 

 J. G. Jack, no. 1329, September 4, 1918. Cultivated specimens: Arnold 

 Arb. (from seed of no. 1329) under no. 17688, September 20, 1923, and 

 May 19, 1925. 



This interesting hybrid was discovered by Professor J. G. Jack in Idaho 

 on the open and rocky summit of Elk Butte. In general appearance the 

 original specimens as well as the plants growing in the Arnold Arboretum 

 have the aspect of a vigorous plant of Amelanchier, and only on closer 

 inspection one may notice the presence of partly pinnate leaves and the 

 compound inflorescence. The flowers, too, with their oblong upright 

 petals look much like those of Amelanchier, but the styles are distinct, 

 and the false partitions of the fruit extend only to about the middle of the 

 locule and are abnormally thick in the sterile cells. 



The parents of the hybrid are apparently Sorbus sitchensis Roem. and 

 Amelanchier florida Lindl. of which specimens were collected on the same 

 date at the same locality; the first species being represented by Jack's 

 no. 1333 and the second by his no. 1332. From Sorbus sitchensis the 

 hybrid is easily distinguished by the mostly simple leaves, smaller, not 

 viscid winterbuds, the smaller paniculate inflorescence with racemose not 

 corymbose branches, the oblong petals, 4-5 styles, and by the dark colored 

 pruinose fruit with long ovate-lanceolate sepals. From Amelanchier 

 florida the hybrid differs chiefly in the larger, more coarsely serrate and 

 occasionally partly pinnate or lobed leaves, in the villous apex of the 

 bud-scales, in the compound inflorescence, shorter petals, distinct styles and 

 in the larger fruit with upright or nearly upright sepals, with shorter 



