4 MISSISSIPPI EXPERIMENT STATION. 



the New York Experimental Station, Geneva, N. Y., for living twigs 

 of Wild Goose Plum and Troth's Early Peach; to Prof. B. D. Halstead 

 for seed of certain varieties of com and tomatoes, and the seed of 

 hybrids; and to Prof. W. W. Rowlee for specimens of Salix cordata, 

 Salix Candida and a hybrid between the two. 



After a description of the external features of each hybrid, the 

 microscopical [structure of parents and hybrids is given in detail. 

 Following this is a more general discussion covering the conclu- 

 sions to be drawn from the study and their relation to certain questions 

 of biological importance. 



The more striking features of hybrids and parents, both macro- 

 scopical and microscopical are illustrated by the accompanying photo- 

 graphs, and photomicrographs. 



Precautions were taken to secure corresponding parts of the differ- 

 ent plants. Parts that varied considerably on account of age, or for 

 other reasons, were not used. The seed was all planted on the same 

 day, plants transplanted the same day, and in so far as possible, the 

 same conditions of soil, cultivation, etc., were provided. 



Historical Review. 



It is said that Linnaeus recognized certain plant hybrids in the 

 wild state and afterwards produced them artificially. From his time 

 to the present, many scientists and particularly, horticulturists and 

 gardeners have produced and studied hybrid plants. Most of ^ the 

 study, however, has been devoted to the external form of the hybrid, — 

 habit, shape of leaves, flowers, relative fertility, etc. But a compara- 

 tively small amount of attention has been given to the study of their 

 microscopical characters. 



Henslow, in 1831, compared a hybrid Digitalis with its parents 

 with a degree of minuteness remarkable for his time. He thought that 

 the morphological characters of the hybrid were exactly intermediate 

 between those of its parents, but that the histological characters were 

 the same in the three plants. Wichura (1865) showed that willow 

 hybrids are intermediate in structure, and Kemer (1878) showed the 

 same to be true of hybrid Pulmonarias. Wettstein (1888) compared 

 the structure of the leaves of four coniferous hybrids with that of their 

 parents, noting especially the general arrangement of tissues. He 

 found that the characters of the hybrid leaves were in most respects, 

 exactly intermediate between those of the parents. MacFarlane (1890, 

 1891, 1900) has probably devoted more time to the study of the minute 

 structure of hybrids than any other student. In 1890 he described 

 the structure of seventeen hybrid Sarracenias, together with others 

 included in his monograph published later. From this study, 

 he was inclined to believe that a hybrid plant contained a blending of 

 parental peculiarities in every cell. These were especially demon- 

 strated in epidermal cells. In 1891 his extensive monograph appeared 

 (MacFarlane 91-a) ; in this work he described the structural details of 

 the following hybrids: Philageria Veitchii, Dianthus Grievei, Geum 

 intermedium, Ribes CulverwelU, Saxifraga Andrewsii, Erica Watsoni, 

 Bryanthus erectus, Masdevallia Chelsoni, and Cypripedium Leeanufn. 



