INTRODUCTION. 



389 



a relatively small outgrowth borne on either the leaf or the stem of the asexual 

 aeration 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 i). In connection with the 

 relationships pointed out by him between the Selaginelleae and Isoeteae on the one hand 

 and the Goniferae 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 Nageli and Leitgeb on the roots of Vascular 

 K^ryptogams, and of Cramer on the apical growth of the stem of Equisetacese and Lyco- 

 )odiaceae, to which numerous more recent observations may be added, have not only 

 :ontributed 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 

 jdition of this book, our knowledge of the alternation of generations has been enriched 

 >y Millardet's discovery of the male prothallium in Isoeteae and Selaginellese ; and the 

 ibours of Millardet, Strasburger, Kny, and especially of Janczewski, have resulted in 

 more complete acquaintance with the development of the sexual organs and of the 

 >rocess of fertilisation itself in its details. 



Taxonomy. Our ideas as to the mutual relationships existing between the various 

 livisions 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 

 fn 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 

 )een proved untenable by Fankhauser's discovery of the monoecious prothallium of 

 .ycopodium. Still a separation of the isosporous Lycopodieae on this account from the 

 leterosporous Selaginelleae and Isoeteae would be unjustifiable. Besides, recent researches 

 lave 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- 

 :ular Cryptogams into Isosporeae and Heterosporeae must be given up as being purely 

 irtificial, 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 

 )lants; 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 

 lelaginelleae 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 

 ly observations and have laid stress upon the distinction of Trlchosporangia from Phyllo- 

 [Caulo-) 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 Fructification of the Higher Cryptogamia, and on 

 the Fructification of the Goniferae, by W. Hofmeister; translated by F. Gurrey ; Ray Soc. 1862, 

 P- 434-] 



^ Luerssen, in den Mitth. aus dem Gesammtgebiet der Botanik von Schenk und Luerssen, 

 Bd. I. p. 107. - 



^ Russow, Vergleichende Untersuchungen, St. Petersburg 1872. 



