16 BULLETIN 289, U. S. DEPARTMENT OF AGRICULTURE. 
covered, not treated, and used as checks in those experiments. 
From the 757 heads covered and not treated in 1911 and 1912 an 
average of 0.1 seed per head was obtained. The relatively high 
average obtained at Altoona in 1911 may undoubtedly be accounted 
for by grasshoppers mutilating the tarlatan which was used to cover 
the heads. On this account heads were occasionally exposed to the 
action of insects for a short time. 
Since no more seed was produced by these heads than may be 
accounted for by insects working on the flowers when they were 
occasionally exposed for a short time on account of rains or grass- 
hoppers, we may say that clover flowers must be pollmated by some 
agency before any seed is produced. 
EFFECT OF SELF-POLLINATION. 
Another experiment was conducted in which the clover heads 
were covered with tarlatan before any flowers opened and were kept 
covered, except while being worked, until mature. As soon as the 
flowers came into bloom they were self-pollmated by springing the 
keels of the flowers with toothpicks, care being taken to rub pollen 
upon each stigma. A separate toothpick was used for each head. 
In 1911, 125 heads were self-pollinated and 170 heads in 1912. An 
average of 0.16 seed per head was obtained in 1911 and an average 
of 0.09 seed per head in 1912. 
The results of this experiment show, as have previous experiments, 
that red-clover flowers must be cross-pollinated in order to set seed 
on a commercial basis. The amount of seed obtained is so small 
that it was probably the result of bees working through the tarlatan, 
although the cytological work reported upon in this bulletin shows 
that it is possible to have an occasional seed produced from self- 
pollination. 
SEED PRODUCTION OF HEADS UNDER ORDINARY FIELD CONDITIONS. 
As a field check on the preceding experiments a number of heads 
were tagged in 1911 and 1912 and neither covered nor artificially 
pollinated. These heads were labeled in different parts of the field 
and Table IV shows the number of heads in each group and the 
average seed yield per head. 
TABLE IV .— Average seed yield of clover heads not covered or artificially pollinated. 
Average 
Number of 2 
Location and year. heads ae 
collected. See 
: head. 
Mines AG 2 er) See TAL Sf pe eee eee a ee 300 50.1 
OPE Ie pee ele ee bates sce Sek cae oe A ee eee 532 50. 4 
DOP ea seme Sac otc ae ts as Seka ed aie See ane ho pete Sere te 47 50.9 
PALOON A LOIS iis 22 spooks Pek jee SoS Ss a eet ce eS ee ee 150 43.6 
PMmessiol2 mote. Tio ass ie ee CE) rae” ie Pe eee 65 53.4 
ee ee ee ae 
