1894. ] The Evolution of the Hepatice. 351 
certainly through critical changes of environment; hence the 
resting-spore. We have here a type of life history where 
continuity commences to curve into a circle and its ends begin 
to unite to form a complete cycle of development. In many 
forms, however, the individual is too hopelessly entangled in 
colony life to be clearly separated. 
{Il. In forms (like Vaucheria) where the sexual cells are 
clearly distinguishable from the early commencenient of the 
process of reproduction, and the oospore results directly and 
simply from the act of fertilization, the life history of the 
plant may be clearly said to be represented by the circle. 
The phase of growth is purely a sexual one from spore to 
germinating filament through the production of sexual ap- 
Paratus to spore again. If asexual reproduction occurs, it 
merely serves to rapidly multiply the plant when favoring en- 
vironment makes it possible, and bears no relation to the 
Sexual process and is not dependent upon it. 
- Among some of the higher alge occurs the simplest 
form of alternation of phases of reproduction. While there 
are various modifications of the process in minor details in 
Many groups of algz, the act of fertilization in certain repre- 
Sentative forms is followed (1) by the formation of a special 
envelop of cells about the oogone as a specialized protective 
Covering, and (2) by the division of the cell contents of the 
gone into a series of reproductive bodies, an asexual pro- 
fess following as a result of a sexual one and therefore de- 
pendent on it. The life history here, instead of representing 
4 simple cycle of growth, can be best characterized as a com- 
bination of two loops each short of a circle, the larger repre- 
senting the sexual stage from germinating spore to the com- 
pletion of the process of fertilization, and the smaller represent- 
ing the asexual phase involved inthe internal cell division that 
results in the development of the reproductive bodies. 
So-called “alternation of generations”, which is nothing more 
= the succession of phases in the life history of the organ- 
™, Commences at a point considerably below the lowest 
bryophytes, 
a. The transition from the above condition to that ses 
st nd in the lowest archegoniates is a simple one The “e 
nce manifests itself in the following particulars: (1) in the 
pit otective envelop of the egg cell being developed prior to the 
* of fertilization and not as a result of it; (2) in the some- 
