48 MISSISSIPPI EXPERIMENT STATION. 



epidermal cells was 9m thick in C. trifoliata, 1 - 2m thick in C. aurantium, 

 while the hybrids are all intermediate; no difference in reciprocal 

 crosses. 



The number, size and shape of the oil glands in the peel differed 

 considerably in the two parent species, while the hybrids in nearly 

 every case possessed an intermediate amount of the character. The 

 characters of the C. aurantiutn parent were dominant in the hybrid in 

 the great majority of cases whether used as pistillate or staminate 

 parent. In all of the characters studied, there seems to be no definite 

 or uniform influence of either parent over any special part. 



Fragaria Hybrid. No part, except leaves of the Fragaria hybrid' 

 was examined. The form and size of the leaves of the two parents and 

 hybrid differed somewhat, but they all seemed to be very similar struc- 

 turally. 



General. 



The limits of characters belonging to species of plants are not 

 definite, or sharply defined. If we examine their structural basis, we 

 find' that they depend upon the number, size or nature of the cells in 

 certain parts of the plant, or in the plant as a whole. Since the number 

 and nature of the cells varies somewhat in different individuals of the 

 species, the characters formed by them must vary and are consequently 

 only relative considering the species as a whole. 



A hybrid character that appears to show pure dominance may 

 upon close examination be found to be intermediate if its structural 

 basis be examined. The xylem of the root of the Radish x Kohlrabi 

 hybrid illustrates this ; the central part of this root when examined macro- 

 scopically, appears to be dense wood, as dense as the wood of the cen- 

 tral part of the root of the Kohlrabi parent, but if this xylem is examined 

 microscopically it is found to have a considerably larger per cent, of 

 thin-walled unlignified cells, thus presenting a structure intermediate 

 between the two parents. There may be a dominance in the size of 

 the whole structure or part, or even in the size of the cells, yet the 

 hybrid tissue may lack in substance or may not have the same chemical 

 composition as the corresponding tissue of the apparently dominant 

 parent. In case of color, too, where the color is due to a dye such as 

 anthocyanin, the presence of half the amount of the coloring matter in 

 the hybrid might produce a color apparently as dense as in the one 

 parent that appears to be dominant in respect to this character. The 

 character may be diluted and the dilution not apparent. Considering 

 all, we are inclined to think that pure dominance is not so frequent as 

 it is commonly thought to be. 



In the plants studied it does not seem that either parent exerted a 

 uniform influence over the whole hybrid or upon any of its parts. In 

 the Nicotiana Tabacum x N. sylvestris hybrid, the greater per cent of 

 Its characters, both morphological and histological, were inherited from 

 N. Tabacum, the pistillate parent. The N. Tabacum x N. alata hybrid 

 shows that the larger part of its inheritance, both in histological and 

 morphological characters, is from N. alata, the staminate parent. Over 

 some characters such as shape and size of leaves, the pistillate parent is 



