} 
1903] DISTRIBUTION OF ISOETES SACCHARATA 197 
so widely separated, which are adapted to its successful growth. 
Not only are difficulties presented by the requirements of its 
habitat, but there are factors in the life-history of Jsvetes saccha- 
vata which are not favorable to rapid dissemination over wide 
areas. Heterospory is one of these. If spores are carried by 
any agency, microspores and megaspores must be lodged at the 
same place or the sporophyte itself must be carried. Besides, 
there seems to be a tendency in the species to dioecism,™ and in 
proportion as this tendency is manifest the difficulties of dispersal 
are increased. 
The means of dispersal upon which this and other species of 
like habitat may depend are several. The most important means 
must always be the water currents, because these are always 
acting at the time and place of spore production. Moreover, 
the chances are very good that the spores so carried may be 
lodged along some shore line where a new colony may be formed. 
In times of storm the waves may tear up whole plants from their 
anchorage in the littoral gravel and carry them far away to leave 
them finally stranded on some beach which may be adapted to 
the growth of the spores thus transported. Late last summer 
the writer saw a thrifty specimen of Jsoetes saccharata floating in 
Chesapeake Bay, 100" east of Stump’s Point, at the mouth of 
Furnace Creek at the head of the bay, over 3*™ from the nearest 
known station for the species, though possibly much nearer to 
some unknown station. 
It is conceivable that biotic agencies might also occasionally 
serve as means of dispersal. Especially, from the observations 
of Charles Darwin and others, we might expect birds which 
frequent the shores to carry the spores occasionally on their feet 
or on their beaks, and as they move from one shore line to 
another, the spores so carried would be left in a new place favor- 
able to growth. A. A. Eaton (zm ditt.) tells me that ducks are 
exceedingly fond of the spores of Isoetes, and that the lamellae 
of their beaks are especially fitted to retain them until washed 
™ PALMER, T. C., 1896, foc. ci#. A.A. Eaton looks upon dioecism in this species 
as of rare occurrence, in which case it would be of slight importance in this connec- 
tion. 
