42 i Report of the Department of Horticulture of the 



Recommendations are given for making tomato crosses and 

 also precautions that are essential for the maintenance and the 

 obtainment of desirable characters. In conclusion, a few sugges- 

 tions are given as to what commercial varieties may be improved 

 by crossing. 



INTRODUCTION. 



That increase of vigor and of size is obtained by crossing plants 

 and animals not too closely related is a well established principle 

 in the biological world. The individuals crossed may be of the 

 same variety or different varieties, and of the same or closely re- 

 lated species ; but the relationship must not be so distant as to 

 induce sterility and weakness. This principle is so well estab- 

 lished that many animal breeders consider the infusion of new 

 blood as a necessity for the preservation of highly prized qualities. 

 Theoretically, if all the characters possessed by a variety or other 

 group of individuals were in a homozygous or pure condition, no 

 inferior individuals would be produced either from the self-fertil- 

 ized individuals or from the ma tings of perfect brothers and 

 sisters ; but unfortunately, this high standard is rarely or never 

 obtained, for all highly organized individuals are made up of 

 many characters, and a combination of only perfect characters in 

 an individual is practically impossible. 



The principle that the offspring of crossed plants are usually 

 more vigorous than their parents was first made prominent by 

 Knight, but the experimental proof of the principle was left to 

 Darwin (10)* who, in his work "Cross and Self Fertilization in 

 the Vegetable Kingdom," built a foundation that still remains un- 

 shaken. Darwin found exceptions to the general law that plants 

 crossed with fresh stock produce offspring of greater height and 

 of greater weight than the self-fertilized plants, a notable example 

 being EschschoUzia calif ornica, its self-fertilized plants surpassing 

 the cross-fertilized plants in height in three out of four cases, re- 

 gardless of the fact that the crosses yielded far more seed than 

 the self-fertilized plants. Perhaps Darwin made this cross be- 



* See Bibliography for reference numbers enclosed in parenthesis. 



