1892. ] 4 Peculiar Case of Plant Dissemination. 325 
the sand plum has advanced from the Arkansas river into 
northern Colorado and Wyoming, since in the scope of the 
buffalo country extending from the forks of Platte river to the 
Rocky Mountains, I have found it only where the main 
buffalo trails formerly existed. Rhus glabra is, however, such 
acosmopolitan shrub, that its dissemination north may be as 
justly ascribed to recent settlement as to the artificial dissem- 
ination we have advocated. 
Again, if the fossil sequoias, figs, magnolias, oaks, palms, 
liquidambars, cycads, salisburias, laurels, persimmons, cinna- 
monums, aralias, sassafras and many other semi-tropical or 
south temperate trees and shrubs now found inthe Cretaceous, 
Eocene and Miocene beds of Colorado, were derived from the 
Arctic regions originally; and if their modified descendants 
now found extant from the Missouri river south to the Mexi- 
can gulf are their living representatives, then it is quite re- 
markable that no representatives of the cactus family occur 
either in Greenland strata or in the same formations in Colo- 
tado. Their total absence also from the Pliocene strata of 
South Park, sorich in Sequoia, Glyptostrobus, Myrica, Rhus, 
Sapindus, Ficus, Planera, Cesalpinus, Acacia, Zizyphus, Ilex, 
ete., though really only negative evidence of their non-exist- 
ence there, is strongly corroborated by the fact that the 
Opuntia is a plant that avoids damp, densely timbered surfaces. 
It delights in dry, stony, sandy soils, and requires but little 
Water the whole year round. The vegetation of the 
Cretaceous, Miocene, Eocene and Pliocene stratain Colorado 
considering, the fleshy nature of the fronds of Opuntia would 
Naturally be very ble to fossilization; but its abund- 
ant seeds of a very hard consistence, would be unusually well 
fitted for preservation, for we find to-day in the strata under 
fensideration fossil nuts of Fagus, Corylus, Carya, Diospytos 
anda species of plum, besides palm nuts, fern fronds with 
‘Porangia complete, seeds of grasses and carices, also of elm 
and Planera. 
lope reader may ask what has all this to do with the ques- 
; n of “‘buftalo pads.” The answer is simple ¢ 
© Prove very strongly by this that the cacti that extend from 
Southern latitudes to Lake Winnipeg, are colonies that in the 
unfavorable tof 
