might be further limited to Grand Tower, Jackson County, where 

 it was first observed by Professor French many years ago. In 

 May, 1902, I found it blooming there abundantly. A limestone 

 ridge called the Devil's Backbone extends for about a mile along 

 the east bank of the Mississippi. Its eastern slope is forested, but 

 its western, receiving the full effect, both of the afternoon sun and 

 of its reflection in the water, presents a succession of vertical sun- 

 burned cliffs, and in their crevices grow the plants of Phlox Stel- 

 laria. Hemispherical tufts a foot in diameter, of dull green leaves 

 and light blue flowers, grow over the face of the cliff wherever 

 there is a fissure an eighth of an inch across. Longer fissures 

 are marked with rows of the plants and a geologist might observe 

 the dip of the strata by noticing the growth of the Phlox. It 

 shows several xerophytic structures, short stiff stems, and narrow 

 coriaceous leaves with inrolled margins. No plant, however, 

 except a pronounced xerophyte, could live on these bare cliffs. 

 Even in May the rocks are so hot that they are uncomfortable to 

 the touch in the afternoon, and in July the heat is still greater. 

 By that time the seeds of the Phlox have ripened and all that re- 

 mains of the plant are the wiry stems and brown leaves. 



Growing with the Phlox are some other xerophytes such as 

 Polvpodium polypodioides, Cheilantlies Feci, Opuntia humifusa, 

 Pellaea atropurpurea, and Solidago Driimmondii. The last two 

 grow especially in pockets in the rock, and a cavity holding no 

 more than a tablespoonful of soil will support a large plant of 

 Solidago or a dozen fronds of Pellaea. This species of Solidago 

 grows in Illinois only along the bluffs of the Mississippi River, 

 and so far as observed, only on limestone cliffs. 



Polypodium polypodioides in southern Illinois is generally xero- 

 phytic in nature, and prefers sandstone cliffs. It may grow, how- 

 ever, on damp shaded cliffs in company with Camptosoms rlrizo- 

 phyllus and Asplenium platyncuron. I have never seen it upon 

 trees in this State. 



Henchcra parvifiora Bartl. reaches in Illinois its northern limit. 

 Its favorite habitat is under a damp sandstone cliff, so shaded 

 that the sun's rays seldom or never strike it. Merc it grows in 

 abundance with Marchantia and other Hepaticae, or an occasional 



