4 Illinois State Laboratory of Natural History. 



some grow on the bark of living trees, a few on the stems or 

 leaves of herbaceous plants, while at least one American spe- 

 cies is found growing over lichens. Some grow in cultivated, 

 even trodden ground, and a very few are aquatic in pools or 

 ponds. 



Size. The variation in size is often considerable; a few 

 forms of Lejeunia are so small as to be almost invisible to the 

 unaided eye; this condition, however, is not common, and most 

 will measure from a few milllimetres to several centimetres in 

 length. All forms are small and inconspicuous, and rarely are 

 the species so crowded or numerous as to form a conspicuous 

 portion of the earth's vegetation. 



Time for Collecting. The hepatics should be collected 

 for preservation and study when in fruit, if this be possible, 

 and this condition occurs at different seasons in the various 

 species; some bear fruit in late autumn, some in early spring, 

 some in midsummer; in short, there is scarcely any season of 

 the year, even winter, that will not find some form in fruit, 

 yet the period from October to May may include the larger 

 number of species for the cool temperate regions of America. 

 Many species have never been found in fruit, and possibly 

 never produce fruit, so it will be advisable to collect all species 

 whether in fruit or not, for otherwise these less known forms 

 may be neglected. 



Geographic Distribution. Too little is known at pres- 

 ent regarding the range of our native species to arrive at defi- 

 nite conclusions regarding distribution, yet certain preliminary 

 features may be noted with even our present knowledge. Of 

 the 231 species described in this paper 111 are common to 

 North America and Europe. We may tabulate our species in 

 five chief groups or natural divisions : 



I. BOREAL: including those species found on the summits 

 of the higher mountains of the Atlantic States as well as the 

 Rocky Mountains of the West, and the colder portions of Can- 

 ada, Labrador and Greenland ; most of the species of this prov- 

 ince are common to the colder portions of the Old World. 



II. MEDIAL: including those species inhabiting that por- 

 tion of the United States and Canada east of the Rocky Moun- 

 tains not; already included in I; more than one-half the species 



