CHAPTER XLII. 
EMBRYOGENY OF THE PTERIDOPHYTES. 
No great difficulty is experienced in recognising the sporogonium of the 
Bryophyta, in its various forms, as the result of the working out of the 
requirements in respect of increasing spore-production and consequently 
of nutrition, under conditions of sub-aerial life. They are believed to 
present a sequence of forms for the most part caught in the up-grade 
of evolution, though showing occasional evidences of reduction.! But in 
the more complex Pteridophytes the case is different: they have, according 
to our hypothesis, proceeded so far in the elaboration of the sporophyte 
that the steps of earlier evolution are less easily grasped: and as the 
area of fact involved is very much greater than in the Bryophytes, and 
the application of the theory of antithetic alternation, with sterilisation as 
a leading feature, has never till now been fully formulated for them, it 
will be necessary to summarise the evidence which has been derived 
from the comparative study of their sporophyte generation. This summary 
will be arranged in order of the events of the individual life, starting 
with the embryology, and proceeding to the vegetative, and finally to the 
propagative system. 
From the criticisms of the older methods of comparative embryology 
advanced in Chapter XIV., it will be gathered that at the moment the 
study of the earliest phases of the individual, as an avenue to an opinion 
on the morphology and phylogeny of Vascular Plants, stands in a dis- 
credited position. Modern analysis has disproved the conclusions drawn 
from the primary segmentation, and shown that there is no constant 
relation between cell-cleavages and the genesis of the several parts. 
1It is possible to make out a case for the converse view of the Bryophytes as a 
series in which the dependence of the sporophyte has been secondarily acquired, and 
reduction widely effective; but that idea is not seriously entertained here, as it is not 
based upon observation o any actually existent organisms indicating that such a progression 
took place: nor has any physiological ground been advanced as a sufficient reason that 
the presumed reduction should have been carried out. 
