INTRODUCTION. 
,3«9 
is a relatively small outgrowth borne on either the leaf or the stem of the asexual 
generation which consists of stem, leaf, and root. 
The proof that what is termed the Moss-fruit, i.e. the sporogonium, is, from its 
position in the alternation of generations, the equivalent of the entire leafy and rooting 
spore-producing plant of Vascular Cryptogams, was brought forward by Hofmeister 
as long ago as 1851 (Vergleichende Untersuchungen, p. 139^). In connection with the 
relationships pointed out by him between the Selaginelleae and Isoeteae on the one hand 
and the Coniferae on the other, this discovery is one of the most fertile in results that 
has ever been made in the domain of morphology and classification. The researches 
of Pringsheim and Hanstein on the development of Rhizocarps, carried out with great 
acuteness and deep penetration, those of Nägeli and Leitgeb on the roots of Vascular 
Cryptogams, and of Cramer on the apical growth of the stem of Equisetaceae and Lyco- 
podiaceae, to which numerous more recent observations may be added, have not only 
contributed to a more accurate knowledge of this group of plants, but have especially 
cleared up the fundamental morphological facts. Since the appearance of the first 
edition of this book, our knowledge of the alternation of generations has been enriched 
by Millardet's discovery of the male prothallium in Isoeteae and Selaginelleae; and the 
labours of Millardet, Strasburger, Kny, and especially of Janczewski, have resulted in 
a more complete acquaintance with the development of the sexual organs and of the 
process of fertilisation itself in its details. 
Taxonomy. Our ideas as to the mutual relationships existing between the various 
divisions of Vascular Cryptogams are at present very variable, they are, in fact, in a 
state of transition. The division into Isosporeae and Heterosporeae suggested by me 
in the first edition and retained in the third edition of this book seemed to be fully 
justified as long as it could be assumed that in the Lycopodieae two forms of pro- 
thallium were developed as in the Selaginelleae and Isoeteae. This assumption has 
been proved untenable by Fankhauser's discovery of the monoecious prothallium of 
Lycopodium. Still a separation of the isosporous Lycopodieae on this account from the 
heterosporous Selaginelleae and Isoeteae would be unjustifiable. Besides, recent researches 
have shown that the Rhizocarpeae are much more closely related to the true Ferns than 
to the heterosporous Selaginelleae and Isoeteae. As a consequence, the division of Vas- 
cular Cryptogams into Isosporeae and Heterosporeae must be given up as being purely 
artificial, and we are led to assume that the differentiation of primarily similar spores 
into microspores and macrospores has taken place in two distinct groups of these 
plants ; for the first time, in a developmental series which begins with the true Ferns, 
for the second, in a series which begins with the Lycopodieae. This assumption is 
supported by the fact that the differentiation of two kinds of spores takes place in 
the Rhizocarpeae in a manner very different from that in which it takes place in the 
Selaginelleae and Isoeteae. Further, since I pointed out in the first edition (1868) that 
the sporangia of some forms arise as multicellular bodies, whereas others are developed 
from single cells, younger botanists (especially Luerssen and Russow) have extended 
my observations and have laid stress upon the distinction of Trichosporangia from Phyllo- 
iCaulo-) sporangia as a point of great systematic importance. 
If, in accordance with the present state of our knowledge, I give up my former 
classification, I must also, on the same grounds, decline to accept the classifications 
suggested by Luerssen^ and by Russow^, for they are based on isolated characteristics, 
^ [On the Germination, Development and Fiuctifieation of the Higher Cryptogamia, and on 
the Fructification of the Coniferse, by W. Hofmeister; translated by F. Carrey; Ray Soc. 1862, 
P- 434-] 
^ Luerssen, in den Mitth. aus dem Gesammtgebiet der Botanik von Schenk und Luerssen, 
Bd. I. p. 107. 
^ Russow, Vergleichende Untei suchungen, St. Petersburg 1872. 
