6 Illinois State Laboratory of Natural History. 



necessary to consider each separately, as the sexual phase, and 

 the sporogony phase. 



Sexual Phase. All HEPATIC^E, in common with the 

 Musci (Mosses), manifest what is called an "alternation of 

 generations,''* which distinguishes them for the most part from 

 the lower forms of plant life, and connects them with the ferns 

 and their allies. The first phase is developed from the spore, 

 either directly or indirectly, and produces the sexual organs by 

 which the second or spore producing phase is orignated. As 

 the sexual phase is the form in which the plant is most likely 

 to be seen, and furnishes the most distinctive generic and spe- 

 cific characters, a detailed account of the various parts and 

 organs will be first given. 



Vegetation. Two principal forms of vegetation are 

 commonly found in this group of plants, namely, the thallose^ 

 consisting merely of an expanded or flattened mass of tissue, 

 without distinction of stem and leaves; and ihefoliaceous, with 

 well marked stem and leaves. These two forms ; however, are 

 only the extremes of a somewhat regularly graded series of 

 forms. The entire series may be characterized as follows: 



1. Forms consisting of a true thallus. (Anthoceros, 

 Aneura.) 



2. Thalloid stems, usually with scales underneath, which 

 may correspond to leaves. (Marchantia, Blasia.) 



3. Pseudo-foliaceous forms, in which the thallus is lobed, 

 the lobes assuming leaf-like forms. (Fossombronia.) 



4. Typical f oliaceous forms. (Jungermania, Frullania.) 

 The vegetation in all Hepaticae is bilateral, that is, differ- 

 ently developed on the upper and under sides. The under side, 

 deprived of the light, differs in internal structure from the 

 upper, and there frequently results a corresponding difference 

 in the external appearance. Most are of some shade of green, 

 the darker more common, but varying to brownish-green and 

 even fuscous; some of the thallose forms are purplish beneath, 



* I have hitherto pointed out the misapplication of this term, which 

 must eventually give place to one more exact and scientific. Compare : 

 Otir Native Ferns and Their Atties, p. 35, note. 



f Frondose is an older term, but the term frond has an entirely differ- 

 ent signification, and is appropriately applied to the ferns; the above 

 term is moreover more expressive and exact. 



