BEARING OF HETEROSIS UPON DOUBLE 
- FERTILIZATION 
DONALD F. JONES 
(WITH THREE FIGURES) 
The increase in development frequently observed in generations 
immediately following a cross in both plants and animals has been 
definitely correlated with heterogeneity of germinal constituents. 
The diverse effects resulting from this heterozygous condition 
have all been included in the one term heterosis (14). Various 
ways in which heterosis in plants may become visible have been 
described by different investigators. An increase in general 
vegetative luxuriance was first recorded by KOrREUTER (11) as 
early as 1766. An increase in the facility of vegetative propagation 
has been shown for hybrids as well as an increased viability under 
adverse climatic conditions (GARTNER 9, and references given there). 
Darwin (7) gives numerous cases in which the rate of growth was 
increased by crossing. Both the time of flowering and maturing 
was hastened, as compared with the parents, in a large number of 
crosses, which also gave an increase in size. 
To these many manifestations of the effects of heterozygosis 
Coins and Kempron (2) have added the fact that in maize the 
endosperm may also be increased in amount as an immediate result 
of crossing. By artificially pollinating maize with a mixture of 
two kinds of pollen, two visibly different kinds of seed were obtained 
upon the same ear (pistillate inflorescence) by taking advantage 
of xenia. The varieties of maize used in making these crosses 
differed among other characters in the color of the aleurone cells 
of the endosperm. A mixture of pollen of a variety with uncolored 
aleurone and of pollen of a variety with colored aleurone, when 
applied to the ear of a plant with uncolored aleurone, gave colored 
and uncolored seeds. In this way 11 ears were obtained, with the 
two kinds of seeds distributed at random. To produce the uncolored 
Botanical Gazette, vol. 65] [324 
