ALFALFA SEED PRODUCTION. ay 
A number of flowers were left untripped on these plants. Less than 
5 per cent of the untripped flowers produced pods. 
The results of both experiments, as tabulated, show that there is no 
definite relation between the age of the flowers when tripped and the 
proportion of pods developed. Clearly there is no diminution in the 
ability of the flowers to become fertilized as long as the flowers remain 
open. 
FORCE NECESSARY FOR TRIPPING. 
Burkill’s results in measuring the force necessary to trip alfalfa 
flowers are thus reported: 
_ That the separation of the basal processes is the legitimate and almost only natural 
method of exploding the flower is obvious from the following consideration. By 
means of a fine wire hung onto the ale, weights to a known extent were suspended 
from them. In September, 1892, flowers obtained near Poulton (Gloucestershire) 
were found to explode with an average weight of 1.68 grams (maximum and minimum, 
2.37 and 0.93). Now, an insect visiting the flower rests its weight on the points whence 
these weights were hung. The worker of Apis I find to weigh about 0.096 and Bombus 
hortorum (large specimens) 0.199 grams. The mere weight of these two insects is 
therefore quite insufficient to explode the flower. Moreover, the pedicel of the 
flower bends under a weight insufficient to explode the flower, so that in these experi- 
ments I found it necessary always to fix the flower by a wire hooked into the standard; 
and, again, the hive bee so settles as to hold the parts of the flowers together with 
its feet. 
By the same method of experiment I discovered that the flower is not always in the 
same degree of explosiveness; the hotter the weather the more explosive is the flower. 
In cold weather the flower frequently remains unexploded for eight or nine days, after 
which it withers, but in hot, sunny weather I found three days to be the maximum 
duration, for explosion is brought about often within 24 hours from the opening of the 
bud. We must remember in this connection that M. sativa is of Persian origin and 
has only traversed Europe northward by slow degrees. 
Shaking by the wind can not explode the flowers. Pieces of paper with a surface 
of 184 and 22 square inches were tied to stalks of this plant in order to give more power 
to the wind, but no effect was observable from the shaking it produced. 
Table XIX gives the results of experiments carried out by West- 
gate with an apparatus similar to that used by Burkill. His results 
confirm those of Burkill in showing that the force required is much 
ereater than the mere weight of bumblebees or other insects which 
trip alfalfa flowers. They also show clearly that the force required 
diminishes as the flowers become older. There is also a considerable 
range of variation in the weight required to trip different flowers of 
approximately the same age. 
1 Burkill,I. H. On the fertilization of some species of pecicaee L.in England. Proceedings, Coucloels: 
Philosophical Society, v. 8, pt. 3, p. 146, 1894. 
