42 
There are however some locations in wnich these difficulties 
are not encountered ; as near the mouth of rivers where the plants 
are left dry by the receding tide ; in places where the water has 
been nearly drawn off from ponds and streams used for manufac- 
turing purposes ; or along the margins of brooks. 
To illustrate the abundance of these plants in eastern Massa- 
chusetts and south-eastern New Hampshire, it might be mention- 
ed that in Seabrook, N. H., a pond usually covering several acres, 
which was so reduced in size by the drought of 1894 that the water 
nearly disappeared, was found to contain such an abundance of 
the quillworts that they formed a nearly continuous green carpet. 
The only species noticed was I. echino&porci Braunii. In October, 
1895, at the head-gate on Powow river at Amesbury, Mass , there 
was noticed floating on the surface of the river inside the gate, 
which at that time was shut but leaking badly at the bbttom, 
such a mass of Isoetes leaves that they might have been collected 
by wheelbarrow" loads. Many of these leaves contained sporangia 
and about all the New England species and varieties were repre- 
sented. At Hampton Falls river, Hampton Falls, N. H., the 
banks on both sides are lined with plants of J. Engelmanni. It is 
probable that many stations of like nature are to be found in Nev r 
England, and in fact in other sections of the country, and that 
they often escape observation. 
It is only in situations fully exposed to the sun that the quill- 
worts are to be expected. Although at times, a fev T scattered 
plants may be found growing in shady places, they are invariably 
few leaved and for the most part sterile, their numbers being main- 
tained presumably by spores brought by the current from more 
favorable localities. 
With a strong lens and some experience, the various species in 
this genus can often be determined, but it seems probable that 
they intergrade at times, I Tuckermani for instance, appearing 
to hybridize with I. echinospora. For any satisfactory work with 
the quillw T orts, a compound microscope is indispensable. Those 
