PART IIE. 
CONCLUSION. 
CHAPTER XL 
ALGAE AND BRYOPHYTA. 
THE general theory which may be based on the occurrence of anti- 
thetic alternation in Archegoniate plants has been expounded in the 
First Part of this book: the Second Part has been devoted to the 
examination of those facts which specially bear upon the theory, as 
they are seen in the several groups of Bryophytes and Pteridophytes. 
It now remains to draw these facts together into a collective statement, 
and to see how far they uphold the hypothetical position: at the same 
time, the attempt may be made to formulate some general morpho- 
logical and phyletic conclusions. It must be remembered, however, 
while doing so, how fragmentary the, series of genera and species, living 
and fossil, actually is, and how incomplete the knowledge of the details, 
especially in the fossils, in which developmental facts can rarely be 
observed. These considerations will restrain any tendency to dogmatism, 
and make such statements as are offered rank rather as tentative con- 
clusions than as matters susceptible of ultimate demonstration under 
present conditions of knowledge. 
It must be admitted at the outset that the theory of initiation of the 
sporophyte—by amplification of the zygote, by repeated cell-division in its 
products, by sterilisation of some of them so as to form vegetative tissue, 
and consequently by deferring of the tetrad-division, with its concomitant 
reduction of chromosomes—is not fully demonstrated by comparison of the 
representatives of any one series of living organisms: there is no known 
phylum which exemplifies all of these several steps ad zuztio. Nor is it 
likely that there should be, if the biological advantage following on the 
multiplication of spores in land-growing organisms were such as has been 
suggested in Chapter VI.; for it is not probable that those land-growing 
organisms in which the sporophyte was nascent would have stood per- 
manently still in the earlier phases of it: the probability would be that 
all surviving forms would have proceeded some considerable length in the 
direction of that biological advantage which follows upon a multiplication 
