10 BULLETIN 104, U. S. DEPARTMENT OF AGRICULTURE. 
pollination and subsequent fertilization when transferred from one 
flowering beet to another, but that they voluntarily travel from plant 
to plant and carry pollen throughout a sustained flight. 
From this evidence there can remain no doubt that these insects 
are capable of playing an important role in the pollination of beet 
flowers. May it not be a veiy significant one \ It is known that hi 
certain parts of Europe and the United States beets have sometimes, 
perhaps frequently, failed to produce seed, although an abundance 
of bloom appeared. It seemed possible that the presence or absence 
of thrips in great number might in part be responsible for this phe- 
nomenon. Subsequent observations, however, afford evidence in dis- 
proof of this theory. It is safe to say that thrips undoubtedly as>i>t 
in the pollination of beet flowers, perhaps to a greater extent than 
any other species of insect. It can scarcely be doubted that they 
perform a like service for many other plants. 
INJURY TO SEED BEETS. 
Thrips feed avidly upon the nectar and pollen of beets, but beet 
pollen is so abundant that unless thrips be present in enormous num- 
bers they apparently do no damage to the floral organs, preferring as 
food the nectar and pollen. However, should they become extraor- 
dinarily numerous, as was the case at Ogden in 1912 during the 
latter part of the season, it would seem that the nectar and pollen 
are not sufficiently abundant to supply their truly voracious appe- 
tites. The}' then attack the more delicate and succulent parts of the 
flowers. Sometimes the styles are cut through at the base, but 
more frequently the papillae, with which the lobes of the stigma are 
thickly studded, are torn to pieces. Furthermore, they may devour 
so much pollen as to interfere with both wind and insect pollination 
by too greatly diminishing the supply. Thrips move actively from 
flower to flower of the same spike, from spike to spike and stem to 
stem of the same plant, and in this way bring about much more close 
pollination than cross-pollination, and in fact effect all the close polli- 
nation and fertilization of which the plant is susceptible. This in 
itself is undesirable and even harmful. Close fertilization has been 
shown to cause degeneration among beets, even in the sense of pol- 
lination and fertilization between different individuals of the same 
proo'env. 
TROUBLE TO PLANT BREEDERS. 
The writer has experiment ally shown that the larvae of thrips in 
all stages readily pass through the meshes of fine silk chiffon and 
much more readily through the net, cloth, and sheeting frequently 
used by horticulturists and plant breeders to isolate flowers designed 
to be hand-pollinated. He has also been able to demonstrate that 
