Form and Structure of Certain Plant Hybrids in Comparison 

 With the Form and Structure of their Parents. 



By harry B. brown. 



INTRODUCTION. 



Notwithstanding the fact that plant hybrids have claimed much 

 attention for many years and have been considered as creations of 

 special interest by gardeners, horticiilturalists, and scientists in general, 

 with few exceptions, only their external or morphological characters 

 have been studied. The histological characters, although numerous, 

 well defined, and fjupdamental to the plant in its organization, have 

 been largely overlooked, and their inheritance not considered. In 

 this investigation, special attention has been paid to the microscopical 

 structure of the hybrids studied and to inheritance of histological 

 characters. An effort was also made to determine whether or not 

 there is a definite relation existing between external and internal char- 

 acters, or a correlation in the inheritance of the two sets of characters. 



In taking up this study, the first task was to produce hybrids 

 between parents as widely separated in histological and morphological 

 characters as possible. To this end the greater part of the summer of 

 1908 was spent trying to make crosses between widely distinct plants. 

 Crosses were attempted between plants belonging to different species, 

 genera and even families. As a result, hybrids were obtained between 

 three very distinct species of Nicotiana, — Nicotiana Tabacum x N. 

 sylvestris, and N. Tabacum x N. alata, and also a hybrid between plants 

 belonging to the two genera Raphanus and Brassica, Raphanus sativus 

 (Radish) x Brassica oleracea var. caulo-rapa (Kohlrabi) . These first gen- 

 eration hybrids, together with plants from self fertilized seed of the 

 parent plants were grown during the summer of 1909. During this 

 stmuner photographs were made, notes and measurements taken, and 

 material fixed and preserved for histological study. Chrom-acetic 

 acid fixer made up after the formula in common use, and Gilson's 

 fixer were used. Most of the material was imbedded in celloidin for 

 sectioning, but paraffin was used in all cases wherever possible. 



In addition to the hybrids mentioned above,, the structure of cer- 

 tain others, was studied in some detail. I am indebted to Dr. H. J. 

 Webber for the fruit of Citrus trifoliata and the fruit of seven different 

 hybrids between Citrus trifoliata and Citrus aurantium; to Mr. J. B. 

 Frost for leaves of a hybrid strawberry plant and also leaves of the 

 parent plants ;^to Mr. Robert Shore for hybrid Calceolaria plants; to 

 Mr. J. W. Kerr of Denton, Md., for living twigs of a hybrid between 

 Wild Goose Plum and Troth's Early Peach; to Mr. M. J. Dorsey of 



