PURE SPECIES AND HYBRIDS OF JUGLANS. 17 



PURE SPECIES AND HYBRIDS OF JUGLANS. 

 LEAVES OF THE PURE SPECIES. 



The English walnut and the eastern black walnut are common in culti- 

 vation in and around Santa Rosa, where they grow thriftily. The Cali- 

 fornia walnut is native at Santa Rosa and is also extensively cultivated as 

 a shade tree in the city, as elsewhere throughout the State. Material for 

 the study of the California walnut {Juglans californica) and the English 

 walnut (Juglans regia) was obtained from trees 16 and 13 meters in height, 

 respectively, which are growing on the grounds of two of Mr. Burbank's 

 neighbors in Santa Rosa. Material of the third type {Juglans nigra) was 

 collected from a second-growth tree, about 10 meters high, which was 

 growing by the roadside between the town of Sebastopol and the Burbank 

 ranch near that place. The collections were made in May, 1907, and May, 

 1908. It is not known whether the trees from which the collections of 

 material were made were the actual parents of the original crosses or not. 

 It is assumed in this study that the alternative is the case. 



Juglans californica. 



The leaves of Juglans californica bear from 9 to 10 pairs of leaflets and 

 1 terminal one (plate l), which is frequently the smallest one of the leaf. 

 The leaflets are ovate lanceolate and taper gradually to the tip; the base 

 is abrupt and even cordate; that of the terminal leaflet is attenuate. They 

 are somewhat roughened on the upper surface and are irregularly serrate, 

 with rather obtuse teeth. A close study of the leaflets would show con- 

 siderable variation, especially in size and in form, although the extent of 

 the variation has not been especially examined. 



In May, 1907, when the first collection of leaves, which were exclusively 

 studied, was made, they were fresh-green and free from fungus; in the 

 following September, when the photographs were made, the upper surface 

 was badly infested with a black fungus which to an extent shows in the 

 plate. 



Juglans nigra. 



The leaves of Juglans nigra are extremely variable, particularly as to 

 size and number of leaflets, which number from 6 to 10 or more pairs and 

 which are irregularly disposed on the rachis (plate 2). In addition to the 

 variation of the leaves as a whole, the leaflets, also, are far from uniform 

 and in outline range from nearly cuneate to ovate; the terminal one is 

 usually the smallest. They taper gradually to an attenuated apex. The 

 bases are abrupt, but usually they are not cordate. The leaflets are serrate, 

 with fairly regular and sharply pointed teeth; the ventral surface, in tex- 

 ture, is generally smooth. 



