INTRODUCTION. 3 



self-pollination, and others have long; stamens, critciata-like , and may be 

 self -pollinated. Thus the hybrid does not in any character revert consist- 

 ently to either parent. This is an example of the first cross breeding true. 



The material for the study of the Jtiglans hybrids was collected at Mr. 

 Luther Burbank's experimental grounds in Santa Rosa and Sebastopol, 

 California, in 1907 and 1908, where, about 20 years before, Mr. Burbank 

 had made the original crosses. 



Juglans calif ornica X Juglans nigra is represented by one tree of the first 

 generation called the ' ' Royal , ' ' and by numerous smaller trees of the sec- 

 ond and third generations, the latter called the "Beeson," in the nursery 

 at Sebastopol. Plates 4, 5, 6, and 9 illustrate, though very inadequately, 

 the variability of the leaves of the first, second, and third generations of 

 this hybrid and show that the greatest range is probably to be found in 

 the second generation, although those of the third are also extremely 

 variable. The young trees of the later generations exhibit also great 

 differences in size, as variation in this regard exceeding 500 per cent has 

 been observed between those of like age and growing under apparently 

 identical conditions. 



Juglans calif ornica X Juglans regia is represented by several trees of the 

 first generation, known as the "Paradox," in Santa Rosa, and by num- 

 erous second and third generation seedlings at Sebastopol. Four Paradox 

 trees are growing in the street in front of Mr. Burbank's residence. Al- 

 though only 17 years from the seed, these trees are about 27 meters in 

 height and their trunks are about 75 centimeters in diameter. The very 

 luxuriant character of the tree is extended to the leaves, which in some 

 instances are surprisingly long and are composed of leaflets which in num- 

 ber and size are said to exceed those of either parent. As will be pre- 

 sented somewhat in detail later in this paper, the leaves are also very vari- 

 able in surface characters, in shape, size, and contour. Certain of these 

 variations in the first and second generation plants are shown in plates 7, 

 8, and 10. 



The hybrids Papaver somniferum X Papaver orientale and Papaver somni- 

 ferum X Papaver pilosum were produced by Mr. Burbank and are now grow- 

 ing at his experimental grounds in Santa Rosa, California. The parents 

 of these hybrids, natives of southeastern Europe, the Caucasus region, and 

 Asia Minor, are either annual (somniferum) or perennial, but the hybrids 

 are perennial. Both of the Papaver hybrids are extremely variable, espe- 

 cially as regards the size, shape, and texture of the leaves and the size, 

 color, and form of the flowers, and they are either wholly sterile (/*. som- 

 niferum X P. orientale) or to a certain degree fertile. On account of the 

 complete or partial sterility of these hybrids only the first generation has 

 been available for study. 



