406 IOWA ACADEMY OF SCIENCE 



so abundant about the middle of the bhiff face. Red cedars are 

 uncommon in this part of the state, this being the only one found 

 in several years' work along the Big Sioux' river in Lyon county. 



The one hundred and ninety bur oak trees (Plate XIV, figure 

 XV) are arranged in two very significant groups, one of which is 

 further subdivided in a characteristic manner. One group is 

 near the top of the bluff, and comprises about seventy individ- 

 uals. They are almost the extreme outposts of the xerophytic 

 trees, crowding up close to the bare prairie. The remainder of 

 the oaks are located chiefly near the middle of the north slope ojf 

 the bluff, and are in about ten small clusters, plainly indicating 

 by their grouping a common origin for the separate clusters. It 

 is probable that a parent tree supplied acorns for each separate 

 group. The great ability of the bur oak to adapt itself to ex- 

 treme variations in humidity and water supply does not come out 

 as strikingly here as in many other localities, for there is a totai 

 lack of these trees on the river bottom. 



There are fifty hawthornes (Plate XIV, figure XVI), all 

 located near the middle of the forest, none of them going as high 

 as the extreme top of the hill, nor as low as the lower third of 

 the hill, and they do not occur on the river bottom. Most of 

 them are found in half a dozen clusters indicating centers of dis- 

 tribution, but about ten are scattered as if planted by birds. 



Three climbing bitter-sweets (Plate XIV, figure XVII) are 

 found near together at the midde of the woods. From their 

 habitat at the foot of trees, they probably have been planted by 

 birds. 



There are about one hundred and fifty wild plum trees (Plate 

 XIV, figure XVIII), none of them found on the river bottom, 

 nor on the lower half of the hill, and nearly all within forty 

 yards of the upper tree limit. They are grouped in thickets 

 indicating their common origin from parent trees, and the method 

 of propagation by suckers and fallen fruit. A very few scattered 

 trees probably have been planted by animals. This tree is one 

 of the hardier of the forest inhabitants, able to endure the severe 

 conditions near the upper tree level. 



Five black walnut trees (Plate XIV, figure XIX) occur, four 

 in one group within thirty yards of the upper tree level, and on© 

 solitary specimen about one-third the way down the hillside. 

 The group of four appear to have a common origin, the seed of 



