MISSOURI BOTANICAL GARDEN BULLETIN 49 
which the stem and branches assume a spherical form, become 
detached from the plant and roll like a ball, scattering the 
seed as they go. Examples of this form of dissemination are 
the Russian thistle, tumbling mustard, and tumble grass. Some 
seeds are provided with buoyant apparatus which permits 
them to be carried by currents of water, many heavy seeds 
being distributed in this manner. Nuts and acorns planted 
by squirrels and birds to provide a future food supply, if not 
found by the animals and if planted in suitable soil and situ- 
ation, germinate. Man has been one of the most important 
agents for the distribution of plants. The Pilgrims who 
arrived on the Mayflower carried with them seeds of herbs and 
ornamentals. Many of these have escaped from cultivation 
and become thoroughly established, sometimes locally, some- 
times over a large territory. All sorts of seed are carried with 
freight, often unnoticed but none the less important. Thus, 
not only from adjacent territory but from distant states and 
from countries across the seas have come those plants which 
we designate as immigrants. These may be divided in two 
groups (1) transients, which establish themselves for a short 
period, then disappear, and (2) permanently established, 
which find conditions congenial and remain indefinitely. 
The following table gives a list of the more important plant 
immigrants of the transient class. For definition of boundaries 
of our local flora, see article on ‘‘Vanished Plants of Our 
Local Flora’’ in the February, 1922, BuLLErIN. 
