362 Bower. — On antithetic as distinct from 
which the asci and ascospores are produced, may be regarded 
as an interpolated stage in the life-cycle ; but all these ex- 
amples might probably be classed with greater propriety 
as instances of analogy, than of strict phylogenetic homology. 
Having recognised that though analogies as regards alter- 
nation are to be found between certain Thallophytes and the 
Archegoniatae, the identity is not a close one, we may now 
return to the consideration of the main archegoniate series of 
Plants : as above noted it is an important fact that in them the 
antithetic alternation is constant, though the balance of the two 
generations may vary : the very constancy of the phenomenon 
makes us enquire why it should be so : the circumstances which 
have led to this constancy seem to me to have been these. 
The archegoniate series is undoubtedly of Algal origin, and 
this their gametophytes amply bear out : they probably sprang 
from filamentous green aquatic forms, inhabiting, as so many 
of the green Algae now do, shallow fresh water, or the higher 
levels between the marine tide-marks 1 : the sexual reproduction 
was effected through the means of external water, and if other 
conditions were favourable it could be effected at any time 
through the water which was always present. Certain forms, 
perhaps thereby escaping from competition, spread to the land, 
where access of water was only an occasional occurrence : 
in these the sexual process could only be effected at time of 
rains or floods, or copious dews, and even then might not 
take place unless the sexual organs were fully mature : thus 
less dependence could be placed upon sexuality for propaga- 
tion, and an alternative method of increase of individuals had to 
be substituted. This was done by the production of the sporo- 
phyte from the zygote : once fertilized a zygote might in these 
plants divide up into a number of portions (carpospores) each of 
which would then serve as a starting-point of a new individual, 
and dry circumstances, under which they would be powdery, 
would favour their dispersion, as in the lower Liverworts. In 
proportion as these plants spread to higher and drier levels 
1 Compare Weissmann’s statement that ‘ the birthplace of all animal and plant 
life lay in the sea.* Nature, 1882, p. 564. 
