1913] ELLIS—SEED PRODUCTION IN YUCCA 73 
least 7oo plants were examined. No seed pods on this year’s 
stalks were found, and conditions were essentially the same as at 
Boulder. About one-half of the plants had flower stalks standing; 
some of which were old and some this year’s growth. Several areas 
were noticed in which many of the plants bore old stalks with empty 
seed pods. Wherever these old empty seed pods were found, it 
was noticed that all the plants bearing them were in a rather 
restricted area (about 100 yards square), and that most of the plants 
within this area bore pods. On the south side of the Republican 
River a group of yuccas was found with seed pods on this year’s 
stalks; 27 plants, all within a rectangle 100 by 200 yards, bore 
seed pods. Only the very small plants, of which there were 33 
within this area, were without seed pods. On the other hand, 
although yuccas grew on both the east and the west of this group, 
no other seed-producing yuccas were found for a distance of 
300 yards or more on either side. Table I shows that the seed 
production in this area was high. 
TABLE I 
Number of Number of pods 
plants per stalk 
Ge. ae ee re ee 
SVN SS OAS catees codecs eee 2 
ee Pe Reena AF ge 3 
| EOE Grrl re ye dey Gn enese ad He 30 4 
Ses ails Wesees Vue CERT CA Cee Cee 5 
Lene eA US EN Cee here hes VEEL Hee ena ed 7 
The data collected show that the seed-producing plants are 
found in occasional small groups. These occasional areas are to be 
explained as the result of a very local, annual distribution of the 
Pronuba moth, the pollinating agent of this species. It is evident 
that a large number of yuccas flower every year, and it is hardly 
Possible that all of these flowers are infertile were they properly 
pollinated. Allowing 10 blossoms to each stalk, it is seen that the 
humber of blossoms produced annually in even a small area is 
very large. This points to an enormous waste by the species as a 
Whole, as a result of the restricted pollination by a single species 
of insect, if the yucca moth is always so locally distributed. So far 
as could be determined, there were no barriers to a flying insect 
