132 NATURE OF FERTILIZATION 



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., be suppressed 

 owing to the influence of other unit characters, 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. Parents of the same kind have 

 the same 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 

 variation in the offspring so that they conform to a more con- 

 stant and uniform type. On the other hand many consider that 

 fertilization is designed to bring about variation in the offspring. 

 So numerous, however, are the traits or unit characters of each 

 parent that it is often impossible at present for the holders of this 

 view to interpret the nature of the variations that sometimes 

 appear in the offspring. More commonly certain characters of 



