8 THE PLANT CELL 



is that, since the male contributed Httle more than a nucleus 

 and the female a relatively large amount of cytoplasm in addi- 

 tion to the nucleus, it must be that to the nucleus have been 

 given the inheritable qualities to transmit from generation to 

 generation; for if the cytoplasm bears these qualities equally 

 with the nucleus the impress of the female might be expected 

 to preponderate in the offspring, (d) In the nuclear and cell 

 divisions resulting in the production of pollen spores and em- 

 bryo-sac spores the number of chromosomes (see Fig. 3) in each 

 nucleus is reduced one-half. The sperm cell and egg cell arising 

 from the germination of pollen spore and embryo-sac spore each 

 contain the reduced number of chromosomes, but when they 

 fuse in the act of fertilization the original number is restored in 

 the fertilized egg and so continues throughout the body of the 

 resulting offspring until pollen spores and embryo-sac spores 

 are again produced by it with the reduced number. What the 

 significance of this halving and doubling may be is told in Chapter 

 XIII, where it is seen unmistakably to relate to the transmission 

 and cooperation of paternal and maternal characters. Since 

 the chromosomes are segments of the nuclear reticulum, the 

 phenomenon here described may be classed as a part of the evi- 

 dence that the nucleus is the bearer of the inheritable qualities. 

 (e) A new line of evidence is at present being opened up in the 

 study of reproduction, and especially in the reproduction of 

 hybrids where the segregation and recombination of parental 

 characters is in harmony with the behavior of the chromosomes 

 during these processes, as told in detail in Chapter XIII. 



The Plastids. — The plastids are distinct and usually rela- 

 tively small parts of the protoplast. They vary in size from 

 barely discernible points with the highest magnifications to 

 discs and bands that traverse the entire length of the cell. In 

 form they may be orbicular, ellipsoidal, disc, or ribband shaped. 

 They are classed under three names according to their color: 

 the leucoplasts are colorless; the chloroplasts contain the green 

 coloring matter chlorophyll; the chromoplasts are yellow, orange, 

 or red. They are, however, really the same thing under different 



