110 MISSOURI BOTANICAL GARDEN. 
high ranges of mountains and connected with Mexico by 
water only through the Pacific Ocean, brings up the inter- 
esting question as to how it came to be there. How is it 
disseminated otherwise than by water currents ? The most 
probable theory seems to be that the plants were carried from 
their southern home, — considering Mexico their original 
habitat, — on the feet of migratory aquatic birds. This is 
very plausible from the fact that if one's finger is thrust into 
a mass of the plants, as they are floating on the water, and 
then withdrawn, scores of plants will be found adhering to 
the surface of the finger. This is probably the case also 
with the legs and feet of ducks and geese. These birds, 
rising from the lakes of the region of central Mexico, where 
Wolffia Ungulata is reported as growing in abundance, may 
start on their long northward journey, and their feet 
folded among the feathers would afford a considerable pro- 
tection to a number of plants which might otherwise be 
dried to death by the rapid passage of the bird through 
the air. Wherever the bird might stop to rest in northern 
lakes, or streams, some of these plants would be washed 
away from it and, if the climatic conditions were favor- 
able, would continue their natural growth. However, it is 
highly probable that later these plants will be found to 
occur at many intermediate points between the City of 
Mexico and the Califomian locality, in which case the 
exposure to the air in the migration of birds would not 
necessarily be of so long duration. In either case the 
plants must have come over the high range of mountains 
to the south of the nowh^ reported habitat. 
My plants were found about three miles west of Bakers- 
field, California, in what is known as the Emery canal or 
Artesian ditch. Concerning this canal, my brother, 
W. O. Thompson, of that place, writes on Feb. 2, 1896: 
** Its origin is similar to that of an artesian well. The 
water comes from the Kern river: but it goes down through 
the coarse sand and rises atraiii some distanc'e from the 
river. The ditch went dry inst -^ciistHi.'" A<^o<.'iated with 
