oe 
_ A. Bigelow on the Freezing of Water. 205 
decurrent along the rachis; in the other leaflets they run out 
rom the whole base. 
5. Dictyopteris Gutb—This genus so well characterized by its 
nervation has still but one representative species, abundantly 
found in the whole extent of our coalfields, Dictyopteris obliqua 
Bunb. The form of the leaves is variable like their size. The 
upper penne are only pinnately lobed and the lobes separated to 
the middle, and short and nearly round. 
Columbus, Ohio, July 4, 1861. 
_ (To be continued.) 
Arr. XXIV.— Observations upon the Freezing of Water at the Pas- 
saic Chemical Works, Newark, N.J.; by ARTEMAS BIGELOW. 
f regular forms, a,b,¢, 
€s to each other, leaving many open spaces O 
-1,whose faces were beautifully 
smooth and perfect, meeting be- 
low from their obliquity. The 
origin of each mass of plates be- 
ing independent of the others, 
and extending from below ob- 
liquely upweled in three or four 
erent directions, a cavity 
would consequently be left be- 
tween the divergent masses, (fig. 
1). These laminee were free, eX Yeni 
cept below, so that a knife thrust y= 
underneath lifted them out sepa- 
Tately, Also as often as the 
thumb was applied with pressure 
their upper edges, the lines 
would disappear and the ice at 
the place of pressure look solid, 
