NATURE OF PLANTS 125 



they have been derived directly from the parent plant by cell 

 division. The gametes derived from the germinating- spores 

 must also contain the same kind of hereditary substances as the 

 parent plants. In fertilization we have the fusion of the gametes. 

 This means that the hereditary substances in the gametospore 

 will be of a dual character since it has been derived from the 

 male and female gametes (Fig. 80). Consequently there is now 

 united in one body, the gametospore, all the possibilities of growth 

 that each gamete inherited from the parent plant. The trans- 

 mission of hereditary characters may also be stated as follows. 

 Every feature of a plant or animal which we recognize in dis- 

 tinguishing them is due to hereditary substances derived from 

 the parents. These substances, possibly lodged in the chromo- 

 somes, cause definite traits (called unit characters) to appear in 

 the offspring. For example, the form of the leaf, the color of 

 the flower, the fragrance of the fruit, etc., are unit characters 

 and each is due to a definite hereditary substance derived from 

 the parents. These unit characters are transmitted by the parent 

 to the offspring. They may fail to appear, i. e., lie dormant, but 

 when active they always cause the same trait or character to 

 appear in the succeeding generation. Offspring derived from 

 parents that differ in possessing one or more unit characters not 

 common to both parents are called hybrids. Hybrids differ from 

 either parent because they have all or only a portion of the unit 

 characters of both parents. Parents of the same kind, i. e., of 

 the same species, have identically similar unit characters and the 

 offspring of such plants and animals must resemble the parents 

 because they only have unit characters common to both parents. 

 For this reason a species is often defined as a kind of plant or 

 animal that is capable of producing offspring like itself. 



At present it is impossible to state the nature and extent of 

 the variations that may result in the offspring from the union 

 of the hereditary substances of the parents. The theory has been 

 advanced that the purpose of fertilization is to lessen the pro- 

 nounced parental traits by blending such characters in the off- 

 spring. In a word fertilization has a tendency to diminish the 

 accentuated traits of the parents and to lessen the amount of 



