450 
Allgemeines. 
But increase of spore-output necessitates increased capacity for 
nutrition and protection of the young spores: the leading factors of 
the advance of the sporophyte to achieve this end have been 1) Ste¬ 
rilisation of potentially sporogenous cells to form somatic tissue: 
2) the Segregation of the sporogenous residue in distinct sporangia, 
and 3) the formation of appendicular organs. The evidence that these 
advances have been effective is found partly in the characters of 
the mature structure in Archegoniate Plants, but more especially in 
the comparative study of their development. It is not held that the 
ontogeny will always serve as a true guide to the phyletic, or mor- 
phological origin, but considerable weight is here accorded to the 
facts of the individual development. 
The first 250 pages of the book are devoted to the general 
Statement of this working hypothesis, its chapters being for the 
most part a series of essays on such topics as Sterilisation, the theorv 
of the Strobilus, Sporangiophores and Sporophylls, the relation of the 
Sterile and Fertile Regions, Embryology, the Symmetry of the Spo¬ 
rophyte, the evidence from Anatomy and Palaeontology, and Am- 
plification and Reduction: while chapter XX gives a summary of 
what has gone before. 
The Second Part of the Book is taken up with a detailed State¬ 
ment of the facts, together with comparison of the constituents of 
the several phyla, with a view to lajfing them out as evolutionary 
sequences. In each case the enquiry has related to all the characters 
of the sporophyte, and that not only of the living but also of the 
fossil types: they are examined as regards their external form, their 
embryology and anatomy, and special attention has been paid to the 
structure and development of the spore-producing members, while 
the characters of the Gametophyte have also been taken into account 
so far as they bear on the main problem. It is found that the con- 
clusions arrived at are supported by general convergence along the 
lines of evidence derived from all of these sources: it has led with 
varying degree of cogency to the recognition of the essentially 
strobiloid origin of all of the main phyla: their differences depend 
not so much upon general plan as on the proportion, arrangement, 
and characters of their appendages, which again have their reflex 
effect upon the vascular System within. Many phyletic conclusions 
follow, such as the near relation of the Ophioglossales to the Sphe- 
nophyllales, and the near approximation of the sporangiophoric 
Pteridophytes together as a coherent, and probably allied group of 
early forms. The Lycopods and the Ferns stand more distinct, 
especially the latter: a scheme has been constructed (p.653), showing 
the somewhat complicated relations of the different groups of the 
Filicales, living and fossil. Such conclusions as these have their own 
value apart from the general theoretical enquiry. 
The Third Part is devoted to general comparisons and con¬ 
clusions. A short chapter deals with the Algae and Bryophyta in 
their bearing on the biological theory of Alternation. A comparative 
chapter is devoted to the embryogeny of the Pteridophytes, from 
which it is established that in all fully investigated embryos the 
axis bears a fixed relation to the very first segmentations of the 
zygote. Other chapters deal with the analysis of the vegetative 
System, the Vascular Skeleton, and the Spore-producing Members: 
it is concluded that the latter, whether sporangia or sporangiophores 
or sori, constitute a category of phyletically uniform parts, probably 
distinct in origin from the bracts, though often supported by them.. 
