96 
ANNE M. LUTZ 
gametic incompatibility is partly responsible for the usual production 
of fewer 15- than 14-chromosome offspring by 15-chromosome forms 
pollinated by 14-, and by selfed 15-chromosome plants. Lata 8 + 
Lamarckiana 7 is plainly an unbalanced combination, but lata 8 -\-lata 
8, assuming that the two gametes combined duplicate chromosomes 
(aa b c d ef g -\- a' a' h' c' d' e' j' could be designated as a balanced 
combination; would these two gametes be compatible? More so 
than lata 8 + Lamarckiana 7 {aa h c d ef g -\- a' h' c' d' e' f g') and 
as much so as Lamarckiana 7 + Lamarckiana 7 (ab c d ef g -\- a' h' 
c'd'e'fg')! 
Whatever the facts regarding these questions it is clear that if 
8-chromosome gametes, capable of functioning, are produced by one 
sex only (barring rare exceptions), as appears to be the case in many 
instances at least, this alone is sufficient to explain the almost complete 
absence of i6-chromosome mutants in cultures of 15-chromosome forms, 
selfed. 
3. The elimination of the extra chromosome by means of one or 
more of the various processes observed by Gates and Miss Thomas 
^2 Gates ('15a, p. 288) commenting upon the fact that 0. lata ruhricalyx produced, 
presumably, only 14-chromosome offspring when selfed and crossed both ways 
with several other forms, said: "Since there was an abundance of pollen, it would 
appear probable that many of the grains must have received the extra chromosome 
and that the latter was frequently lost during the divisions in the pollen tube." 
Gates's suggestion is well worth considering, but we should not overlook other 
possibilities in the case. While Gates and Miss Thomas ('14, p. 545) tell us that 
lata ruhricalyx "produced a good amount of viable pollen" and that it "developed 
long stout capsules" (p. 533), thereby indicating that seeds were produced in abun- 
dance, Gates ('15a) further states that few offspring were obtained from crosses of 
this mutant both ways with several other forms. Since 15-chromosome forms com- 
monly produce very little pollen capable of functioning, or none at all, it is probable 
that these plants were 14-chromosome forms; however that may be, let us assume 
that only 7-chromosome eggs, capable of functioning, were produced by lata ruhri- 
calyx. Even though well-filled fruits were developed, if only relatively few of the 
large number of seeds produced succeeded in germinating, perhaps those resulting 
from 97 + a' 8 unions were incapable of germinating, or failed to germinate in the 
time allowed them. Perhaps one of the 15 male chromosomes was eliminated oc- 
casionally during reduction by one or more of the numerous irregularities observed 
by Gates and Miss Thomas in this form, such as failure to be included within the 
heterotypic daughter nucleus and subsequent degeneration; degeneration on the 
homotypic spindle, etc. In this way many more 7- than 8-chromosome pollen 
grains may have been formed. We have no assurance that every seemingly good grain 
is capable of functioning; neither can it be said, because 15-chromosome offspring have 
not been found in cultures of 0. Lamarckiana pollinated by certain 15-chromosome 
