CYTOPLASMIC INHERITANCE 223 



arise the checkered seedlings from which white or green 

 branches grow out. 



The preceding facts and theories relating to plastid 

 inheritance show that if any element outside the nucleus 

 has the power to propagate itself it may be transmitted 

 through the egg, and even possibly through the sperm 

 (pollen) also. There is no contradiction here iii any 

 sense to Mendelian inheritance but only an additional type 

 of inheritance that can be studied by as exact methods 

 as those used in Mendelian work. The chief difference 

 between chromosomal and plastid inheritance lies in the 

 orderly sequence of the distribution of the genes in all 

 divisions by means of the mitotic figure, whereas the plas- 

 tids are supposed to be shuffled about at random to the 

 daughter cells (partly because their division period does 

 not correspond with that of the cell). This haphazard 

 distribution of the plastids at any and all divisions is in 

 striking contrast to the sorting out of the genes that occurs 

 only at one specific cell-division when the germ-cells pass 

 through the maturation stage. Hence the orderliness of 

 Mendelian inheritance as contrasted with the more irregu- 

 lar procedure in plastid inheritance. 



To embryologists familiar with the fact that differen- 

 tiation of the egg is closely associated with the cleavage 

 pattern, it was a natural inference that in the cytoplasm 

 lay the inherited characteristics that gave form to the 

 embryo, and even to all of its essential features. Little 

 room would seem to be left for the action of the chromo- 

 somes except to fill in the details of the characters already 

 outlined by cytoplasmic activity. This view might l)e la- 

 conically referred to as the theory of the ^'Embr^^o in the 

 Rough, '^ or more generally as the *' Theory of the Organ- 

 ism as a Whole.'' Boveri discussed some such view 

 (1903), and at first considered it favorably. It has since 

 been seriously discussed by others. Boveri pointed out 

 that when a horse is crossed to an ass it makes no differ- 

 ence which way the cross is made, for both egg and sperm 



