402 IOWA ACADEMY OF SCIENCE 



torn, and crowding can play no part in the distribution on the 

 river bottom, because the forest there is thinly scattered. In 

 place of over-crowding there, we have the river floods acting 

 as a destructive agent when they periodically inundate this land. 



Nearly twelve hundred bass wood trees (Plate XII, figure 

 VII) grow in the region studied. None of these are found on 

 the river bottom. On the bluff face they are scattered quite 

 regularly from almost the foot of the bluff to within a distance 

 of two to five rods of the upper tree limit, with the exception 

 of an area about five rods wide a little below the middle of the 

 forested tract. A most noticeable thing with the bass wood is 

 the "family group," as it might be called, in which a consid- 

 erable number of individuals are clustered about the grave of 

 the parent from which they sprang. While the bass wood is 

 able to adapt itself to great variations in growing conditions, 

 it shows plainly by its development the influence of those con- 

 ditions, as the largest and tallest trees are found near the foot 

 *of the bluff, where they are well protected. A large number 

 of the trees at the upper limit of their growth do not run more 

 than one or two inches in diameter. 



There are three hundred eighty-two gooseberry bushes (Plate 

 XIII, figure VIII) in the tract. None of them occur on the 

 river bottom, but they are distributed with a fair degree of 

 equality from the foot of the bluff almost to the upper limit of 

 the forest, with the exception of several large spaces a little 

 below, and also a few a little above, the middle of the forest, 

 where they are probably crowded out by other vegetation. 

 In some cases, groups of these bushes indicate by their arrange- 

 ment that they are from one parent plant. 



There are eight elder bushes in this tract (Plate XIII, figure 

 IX), loeated in two groups not far apart, near the mouth of 

 a gully at the bottom of the bluff, where they are well pro- 

 tected, and receive abundant moisture. The arrangement of the 

 members of these two groups is such as to show that each group 

 is from a single parent that formerly stood at this spot. We 

 may attribute their absence from the river flat to the flood 

 waters of the river, and their absence from the upper parts of 

 the wooded bluff to insufficient moisture. 



There are sixteen choke-cherry trees (Plate XIII, figure X), 

 one group of which is found on the escarpment at the foot of the 

 bluff, about ten feet above the river flat. These are in a close 



