No. 551] NOTES AND LITERATURE 



685 



is strongly on the side of their direct derivation from some liver- 

 wort-like ancestor. It is this question that makes a thorough 

 study of the liverworts of such great importance in seeking for 

 an explanation of the origin of the vascular plants. 



Aside from this, however, the Bryophytes, especially the liver- 

 worts or Hepaticas, are exceptionally interesting, as they show in 

 a remarkably clear way many adaptations to special environ- 

 mental influences. 



The Bryophytes are divided, usually, into two main groups— 

 the Liverworts (Hepaticae), and the True Mosses (Musci). One 

 peculiar order, Anthocerotales, the "Horned Liverworts," is 

 sometimes considered to represent a third class, coordinate with 

 the Musci and Hepaticae. Cavers does not accept this view, but 

 considers them to represent an order only of the Hepaticae. 



Aside from the Anthocerotales, the liverworts usually are 

 divided thus into two orders, Marehantiales and Jungerman- 

 niales. There are, however, several genera that to a certain 

 extent combine characters of both of these orders and sometimes 

 have been assigned to one, sometimes to the other. Of these 

 genera Sphcerocarpus may be cited. This is, on the whole, prob- 

 ably the simplest known liverwort, and is represented in the 

 United States by several species in the warmer parts of the 

 country. Much like Sphcerocarpus is a peculiar liverwort, 

 Geothallus, known as yet only from San Diego in Southern Cali- 

 fornia. A third genus, Eiella, evidently related to these, is an 

 aquatic type, only recently found in America. All of these are 

 very simple liverworts and probably stand near the base of the 

 liverwort series. They may, perhaps, be regarded as synthetic 

 types connected with both of the main series of liverworts. 

 Cavers proposes to unite them into a special order, Sphaerocar- 

 pales, and this conclusion will probably be accepted as repre- 

 senting best their position in the system. In the Sphaarocar- 

 Pales, as interpreted by Cavers, the sporophyte or neutral gen- 

 eration is of simple structure, and the elaters which in the typical 

 liverworts accompany the spores are represented by undiffer- 

 entiated sterile cells. 



From some form probably not very unlike Sphcerocarpus, but 

 with perhaps a still simpler sporophyte, it is probable that the 

 two lines of development, the Marehantiales and the Jungerman- 

 niales have diverged. Within these two orders the course of 

 development can be easily traced, as nearly all the stages in the 



