234 REPRODUCTION 



it actually happens, four different combinations would result 

 as suggested by the pointing arrows in Fig. 133, where at A is a 

 row of sperm cells, at B a row of egg cells, and at C a row of 

 fertilized egg cells. From this it would follow that, on the average, 

 in every four plants of the second generation after the first cross 

 (in F^), one would possess only maternal inheritance for any 

 specific character, one only paternal, and two would be hybrids 

 like all the plants of the first generation. Since lateral flowers 

 are dominant over terminal, fertilized egg cells 2 and 3 would 

 produce lateral-flowered plants as well as would 4 which has only 

 lateral flowers in its constitution. 



Mendel's explanation, it will be seen, agrees perfectly with the 

 results obtained from his experiments (see Fig. 132). 



Paternal and Maternal Chromosomes. — Let us now turn 

 back to Fig. 126, E to I, where attempt is made to show what 

 happens to the chromosomes during the divisions of grandmother 

 and mother cells of microspores and megaspores. Under the 

 microscope it can be seen that chromosomes divide and become 

 distributed as shown in the figure, but it is impossible, at least 

 in most instances, to tell from their appearance that half of them 

 are paternal and half maternal. That they are this we conclude 

 from Mendel's experiments, that is, the results of these are pre-^ 

 cisely what would follow if the chromosomes become segmented 

 into paternal and maternal kinds as represented in the figure. 

 Therefore, when it is said that half of the microspores and mega- 

 spores are paternal and half are maternal for a definite character, 

 let it be understood that the conception is based on direct ob- 

 servation through the microscope of processes in the formation 

 of these spores, and on the kinds of progeny resulting from a 

 union of their gametes (sperm and egg cells). 



We must now take note of a fact observable in Fig. 132. The 

 crossing of the lateral- and terminal-flowered peas seems to have 

 given rise to nothing new, the progeny are in appearance exactly 

 like one parent or the other; the only evidence that a cross has 

 taken place is found in the fact that half of the individuals (6 and c 

 under Fj) show their hybrid origin by producing two kinds of 



