Theory of Antithetic Alternation of Generations. 127 
on the gametophyte. He dismisses in a slightly contemptuous 
paragraph at the end of the chapter the view that it might have 
been free-living throughout its life, as it is in Dlctyota. It is only 
necessary here to remark that such a hypothesis is not primd facie 
ridiculous, but at the same time it is no necessary complement of 
the view that the sporophyte was originally a thallus and not a 
sporogonium. Professor Bower does not definitely commit himself 
to any theory of the phylogenetic origin of the root. He merely 
states the alternatives that it may have “ resulted from the trans¬ 
formation of a leafy shoot by loss of the appendages, followed by 
other special adaptations in relation to its life, and to its absorptive 
function in the soil ” ; or that “ it arose as a new type of haustorial 
outgrowth, not originally of shoot-nature.” He is inclined to accept 
the latter alternative. The phylogenetic position of the “ protocorm ” 
is then considered and the conclusion reached on good grounds that 
it probably does not represent an ancestral phase of embryonic 
structure even for the genus Lycopodium as a whole. With the 
author’s general conclusion that the origin of the root-system of the 
sporophyte is “ quite as obscure as that of the leafy shoot itself ” we 
agree, but would suggest that the difficulty is made less by supposing 
the root to represent a thallus-branch which shared the characters 
of the aerial branches of the primitive sporophyte and has retained 
such of them as are adapted to its life conditions and functions. 
The “ rhizophores,” and similar structures whose morphological 
nature has always been a difficult problem, would then appear as 
modifications of the primitive type of branch, and the difficulty we feel 
of understanding why a “haustorium” should “resemble the shoot 
from which it arose in its structure and in the character of its 
branching ” would be removed. This kind of difficulty is inherent 
in the attempt to derive a plant from a sporogonium, and can only 
be met by more or less gratuitous hypotheses. 
In discussing “ the evidence from Palseophytology ” the author 
calls attention to the fact that the fossil record is silent on all 
questions relating to the “ prime origins ” of the leafy sporophyte, 
this being no doubt largely due to the fact that this origin must 
have taken place long before the earliest rocks from which fossils 
are recorded were laid down. There are nevertheless certain 
palaeontological facts, already alluded to, which, so far as they go, 
certainly do not tend to support the “ strobiloid theory.” There 
is the early existence of relatively megaphyllous plants belonging 
to or allied with the Equisetales, and there is the entire absence 
of any fossils suggesting relative microphylly among the earliest 
known Ferns. 
In analysing the factors causing “ amplification and reduction” 
in the course of evolution, Professor Bower shows reason to believe 
that the latter process has been over-rated in the discussion of the 
relationships of more or less isolated forms, and very rightly points 
out that good grounds should be assigned for invoking a general 
process of reduction in any given case. The mycorhizal Pterido- 
phytes he thinks show little evidence of a general replacement of 
autotrophy by heterotrophy such as would involve any considerable 
reduction of the chlorophyllous system. In certain cases he sees 
an increasing dependence of the sporophyte (or sporogonium) upon 
the gametophyte, leading to an effective reduction of the assimilatgry 
apparatus of the former. 
