198 BOTANICAL GAZETTE [SEPTEMBER 
out in another locality, and he thinks that this has been perhaps 
the efficient means of their dispersal. 
A third possible method of dispersal is transportation of 
spores by the wind, but it is evident that successful dispersal by 
this means must be very rare. In the first place, the wind could 
only secure spores to carry after they had been stranded on the 
shore at high tide or in times of storm. Besides, the winds 
almost invariably blow across the shore line instead of parallel 
with it, so that the likelihood of the spores being stranded ina 
place adapted to their development is very slight indeed. 
' As the distribution of Jsoetes saccharata appears to be limited 
by the confines of Chesapeake Bay, while the agency of birds 
and of the wind are not so limited, these agencies must be 
assumed to be relatively inefficient. For, if the waterfowl pro- 
vided efficient means of dispersal, we should expect to find the 
species following the chief lines of migration as far as there 
were suitable habitats for its growth. As these lines of migra- 
tion run parallel with the Atlantic coast, this would specially 
favor the transportation of J. saccharata into Delaware Bay and 
of I. riparia Engelm. into Chesapeake Bay. Our failure to find 
evidence of any such transportation is peculiarly striking when 
we bear in mind that the Back Creek station for /. saccharata is but 
little more than 16“ distant from the nearest point on Delaware 
Bay, while the known stations on Chesapeake Bay are in some 
instances separated by distances of more than 80‘. 
We must conclude from these facts,?3 I think, that water cur- 
rents supply the only efficient means of dispersal for this species, 
and that these have supplied the means by which new colonies 
have sprung up in more or less distant areas. But even water 
currents could scarce be adequate to carry the spores from one 
3This entire discussion is based on the assumption that /soe/es saccharata and 
/. riparia are really distinct AS as sia ave always been considered. In some 
of its forms J. saccharata a aches so nearly to Z. bance! that the suggestion is not 
far that nae are ecological aidiien of the same species oo little is known, as ber 
about ecological varieties, to make more than a eae ee permissible. is 
obvious that successful transportation from the one bay to the other may have ate 
place any number of times, if in each case the ecological conditions were such as to 
produce from the spores of a single specimen, /. riparia in Delaware Bay and / 
saccharata in Chesapeake Bay. 
