672 
GENETICS: BAB COCK AND COLLINS Proc. N. A. S. 
from a pure tectorum achene of the same size would not be surprising but 
that the cotyledons coming from the much smaller capillaris achenes 
should be so much larger than those usually coming from ordinary capil- 
laris achenes seems unusual and gives immediate evidence of the hybrid 
nature of the seedling. 
The hybrid seedlings grew very vigorously through the cotyledon stage, 
then growth and development ceased although different plants remained 
alive from 30 to 81 days in this arrested condition. All hybrids died 
before passing beyond this stage of development. The attempt to grow 
the hybrid between these two species was made three separate times 
always with the same behavior and the same results. 
Tabulation of Rbsui^ts of ReciprocaIv Crosses 
CULTURE 
NO. 
PARENTS 
COTYLEDON 
CHARACTERS OF 
HYBRID 
BEHAVIOR 
OF HYBRID 
NUMBER 
OF SEED- 
LINGS 
Z3 
capillaris X tectorum 
6 tectorum, 
5 capillaris, 
1 intermediate 
all failed to pass 
cotyledon stage 
12 
Zs 
capillaris X tectorum 
all tectorum; showed 
hybrid vigor 
all failed to pass 
cotyledon stage 
6 
Z 7 
capillaris X tectorum 
all tectorum; showed 
hybrid vigor 
all failed to pass 
cotyledon stage 
3 
Z8 
capillaris X tectorum 
intermediate 
failed to pass 
cotyledon stage 
1 
Z 10 
tectorum X capillaris 
all tectorum; showed 
hybrid vigor 
all failed to pass 
cotyledon stage 
12 
Z 12 
capillaris X tectorum 
small and distorted, 
abnormal 
failed to pass 
cotyledon stage 
1 
Z 13 
capillaris X tectorum 
small and distorted, 
abnormal 
all failed to pass 
cotyledon stage 
5 
Histological examination of a hybrid seedling revealed a most unusual 
teratological condition of the tissue systems and of the cells which, no 
doubt, was the immediate cause of the unusual behavior noted. These 
tissue systems were in a chaotic condition where order and continuity 
should be expected. Patches of embryonic tissue were scattered irregu- 
larly among the vegetative cells, patches of tracheary cells were likewise 
found here and there in the meristematic tissue of the seedling. In fact, 
tracheary cells were in one section found to be extending at right angles 
to the long axis of the seedling. Groups of vegetative cells were separated 
by streaks of disorganized and disintegrating tissue. Some of the vege- 
tative cells were abnormally large. 
In this interspecific hybrid it appears as if the force directing cell differ- 
