240 ON TRAPA NATANS. 
spines of some other species (viz., 7. guadrispinosa, Roxb., and 7. 
bispinosa, Roxb.). ae 
In regard also to its geographical distribution, 7rapa natans shows 
iariti At the present time i 
plant has not commenced at a recent period is manifest from this fact, 
that the fruit of it in a half-fossil state has been found in the turf in 
localities where the plant, as far back as we now, has not been 
living—for instance, at Gallemosse in Lolland, a Danish island, accord- 
1858, pp. 121—26), and in turf at N asbyholm in Scania, according to 
A. G. Nathorst (Kongl. Vetenskaps Academiens Forhandlingar, 
1872, p. 133). 
It is a matter of some difficulty to trace out the causes of the 
oe of this plant ; probabl they are various, and not the 
m N 
from the north of Europe, where a diminution in mean temperature 
might have produced the reatest influence on its occurrence, but also 
