94 
ANNE M. LUTZ 
but fewer than 28, chromosomes commonly produce no pollen, very 
little, or at most, only a moderate amount; furthermore, one ordi- 
narily finds that very few of the grains produced are normal appearing, 
hence the majority are probably incapable of functioning. On the 
other hand, 14- and 28-chromosome plants not only produce larger 
quantities of pollen, as a rule, but usually a much larger percentage of 
the grains produced are normal appearing. In the case of 14-chro- 
mosome forms, usually about 60-70 good appearing grains per 100 
(sometimes fewer, sometimes more) are found in the early and mid- 
season buds. These factors are undoubtedly primarily responsible for 
the difficulty commonly experienced in obtaining seeds from forms 
having (14 -i — 28)*^ chromosomes, as compared with the relative ease 
with which they are ordinarily secured from 14-chromosome forms, 
selfed, or even from selfed 28-chromosome plants; but it does not tell 
us why seeds of 21 -chromosome forms, when secured, germinate 
much less readily than seeds of 14-chromosome plants and less readily 
than those of 28-chromosome 0. gigas de Vries. 
Gates ('15a, p. 194) says: "It is clear that triploidy leads to the 
production of many new chromosome-numbers, through the irregu- 
larities it introduces into the meiotic phenomena. . . . It is at present 
unknown whether the number alone determines the viability, or 
whether particular chromosome combinations will, owing to incom- 
patibility, fail to produce an .embryo after fertilization." Elsewhere 
(p. 234) he speaks of the difficulty experienced in making ''giant 
crosses" (doubtless referring to crosses of 28- with 14- and 15-chromo- 
some forms) and says: "This is undoubtedly a result of the unbalanced 
chromosome numbers and the meiotic irregularities to which they 
lead, , . . ." 
The writer has long thought it probable that the incompatibility 
of certain combinations, particularly such as those brought about by 
selfing triploid forms, is partially responsible, not only for the small 
number of seeds produced, but for the relatively small number of seeds 
which germinate. Doubtless many of the heterotypic distributions 
in triploid forms (20- and 22-, as well as 21 -chromosome individuals) 
are irregular, resulting in the production of daughter groups with 
fewer than 7, more than 7, regular 7, or, possibly, an irregular assort- 
ment of 7 chromosomes. Even such combinations as 10 -j- 10, 10 -f 1 1 
and II +11 in selfed 21-chromosome forms may be less compatible 
" More than 14, but fewer than 28. 
