170 ILLINOIS STATE ACADEMY OF SCIENCE 



still greater soil moisture, is to be found as well on sites 

 that are so much drier as to make the species unreliable 

 as an indicator. 



In Oregon township, section two, there is a stand rep- 

 resentative of mesophytism and xerophytism condensed. 

 Here Quercus alba, Q. macrocarpa, Hicoria ovata, Quercus 

 rubra, Hicoris minima, Tilia americana, Ulmus pubescens, 

 Prunus serotina, P. virginiana, and Juniperus virginiana 

 are intermingled. It is of course, a response to the physio- 

 graphic arrangement, large differences taking place in small 

 distances. 



Two of the more unusual species of oaks, out of a total 

 of seven noted by the writer in the region of the Rock 

 River woodlands, are Quercus acuminata and Q platanoides. 

 The latter is seen chiefly on some of the islands, while the 

 former has two different forms and occurrences. It is 

 found in a mesophytic stand, as upon the west shore of the 

 Rock north of Oregon at the place known as the Narrows, 

 at the foot of a wooded talus and on the inner part of the 

 adjacent flood plain. Here Q. acuminata has the form of 

 very thin, chestnut-shaped, acutely lobed leaves, and is a 

 tall straight tree. It is to be found also on limestone 

 ridges, which may be furnishing rather dry or rather 

 moist habitats. Here the species is a short tree, or at 

 least not tall and straight, with very much smaller leaves 

 that are considerably thicker and inclined to be lighter in 

 color on the under surfaces, while nevertheless preserving 

 the acutely lobed and chestnut shaped outline. These two 

 types are so distinct in appearance as to seem different 

 species. In the location at the Narrows Quercus acuminata 

 occurs with Acer saccharum, A. saccharinum, Robinia pseu- 

 dacacia, Juglans cinerea, Salix fluviatilis, and Populus del- 

 toides, as the tree species, and Alnus incana and Cornus 

 paniculata as characteristic shrubs. Mesophytic herbs con- 

 stitute the ground cover. Consequently there is a telescop- 

 ing or condensation, a combination of the typical streamside 

 association with the woodland oak-m.aple climax, with 

 Quercus acuminata as the ecological equivalent here of 

 Quercus rubra. Alnus incana is, of course, common along 

 streams, though the genus is not especially frequent in Ogle 



