152 BROOKLYN BOTANIC GARDEN MEMOIRS 
TABLE I1—Continued 
Cases Fertile in Group Cases Sterile in Group 
Group | Ped. No. 
| | BA Cal | ee eal ie on aie ee D| Baie 
| | iN 
Cee: 16 5 | © I I - | oO One fo) (e) - 
1G) Ata\t (2 eO I - | - O Onis 0 |) 
| 26 G20 r|/-/]- o |) S07 )4 > 0, See 
28 Oleh sO oe a oO 0} 4) | = | = 
2 9 6 | oO = = = O Or 4 = = = 
31 I By Oro ee I O-le3 -/|-|]- 
ee Me eee me eee Os coelp se ees = | = 
44 Ty | 125| 90 I I I I @:| 7 || 0: | ouimias 
Vio 3 Sigma ae amet Coa I - O One -}|o]- 
De epee ZOOM O UE sOr ly orcleas oO I - oO ONE Co) 0; | ‘Oral 
ne 43 | SS ae (er. 0") so. Eos! eo.4|\ om cms 
| Ora ee II CMI f Reel - = (0) oO o| Oo - | - O 
reciprocal, Cross No. 2. In the classes A, B and C the proportions 
were 18, 10, 10 and 4, 6, 2 respectively. This similar behavior of the 
progeny of reciprocals seems to us strong corroboratory evidence in 
favor of the conclusion that reciprocal crosses always behave in like 
manner as regards self-sterility. 
The study on this family is but one of several that have been 
made. but we believe that the data on it alone show unmistakably that 
the behavior of self-sterile plants in intercrosses is governed by a 
relatively small number of factors which act through pollen as if the 
pollen grain possessed the characters of the sporophyte from which it 
came, and that the gametes of plants having like constitutions as re- 
gards effective factors are incompatible in the sense that they do not 
make a normal pollen-tube growth and hence do not reach the ovary 
in time for fusion to occur. This interpretation shows both why 
plants are self-sterile and cross-sterile. It accords completely with 
the fact that a population of plants may be divided into groups on the 
basis of their mating proclivities and that each member of any group is 
cross-sterile with every other individual of that group although it is 
fertile with every individual of every other group. 
These assumptions being true, it ought to be possible by con- 
tinuous self-fertilization, utilizing end-season pseudo-fertility, to 
obtain ultimately a population in which every individual possesses 
the same effective self-sterility factors. In such a population all of 
the plants will not only be self-sterile, but will be cross-sterile. Sucha 
population has been obtained. 
