TRANSACTIONS OF SECTION K. 1057 



may admit of a decided answer. It can, however, hardly fail to be produc- 

 tive of good if this discussion enables us to see our way more clearly to the 

 directions in which the answers to these problems must be sought. 



(b) On Alternation of Generations in the Thallopliytes. 

 By Professor Georg Klebs. 



[Ordered by the General Committee to be printed in extenso.'] 



Since the pioneering investigations of Hofmeister it has been generally recognised 

 in Botany that the Archegoniatse are characterised by a definite form of alterna- 

 tion of generations. It consists in the regular alternation of a part which bears 

 the sexual organs — the gametophyte — and of a non-sexual part which produces 

 tlie spores — the sporophyte. An essential difference separates the two divisions of 

 the Archegoniatee. In the Pteridophyta the gametophyte is a delicate, short- 

 lived, thalloid structure, the sporophyte is a well-developed, leafy plant. In the 

 Bryophyta, however, the gametophyte appears as a leafy plant, while the sporo- 

 phyte is represented by a leafless stalked capsule, which lives as it were parasitically 

 on the gametophyte. 



In sharp contrast to the harmonious unanimity which has hitherto been the rule 

 in Botany as regards this alternation of generations in the Archegoniatse is the 

 lively contest of contradictory views as to the alternation of generations in the 

 lower plants. With regard to these the question arises, first, whether a regular 

 alternation of definitely characterised generations is to be observed, and secondly, 

 what in that case is the connection between this alternation, should it turn out to 

 he a fact, with that of the Archegoniatfe. I shall not deal exhaustively here with 

 the many different opinions on this question ; I shall briefly touch upon those 

 views only which are important in point of principle. 



The first clear carrying out of the idea of a regular alternation of generations 

 in the Thallophytes is in the Text-book of Sachs (1876), who there endeavoured to 

 make the course of development of Algse and Fungi fit with that which liolds in 

 the Mosses. The life of Vaucheria, Mucor, an Ascomycete, or one of the Floridete, 

 is divided according to Sachs into two sharply separated parts, of which one is 

 characterised by the appearance of sexual organs, the other by the spore-bearing 

 tissue which springs from the fertilised ovum. Thus the mycelium of a Mucor 

 which bears the sexual organs, the thallus of Vaucheria, or of the Floridefe, repre- 

 sents what we now term the gametophyte ; the fruit body of Ascomycetes, or of 

 Floridese, the zygospore of ilfwcor, the oospore of F«itcAe?7'«, represent the second 

 non-sexual generation — the sporophyte. The alternation of generations of the 

 Thallophytes is therefore according to Sachs essentially similar to that in the 

 ArchegoniatfB. The propagation by zoospores, conidia, etc., corresponds to the 

 propagation by buds in the Mosses and Ferns, and is not taken into account as 

 regards the actual alternation of generations. 



Pringsheim takes up a quite opposite point of view (1876, 1878). According 

 to his opinion the fruit of the Ascomycetes and Florideas has not the value of a 

 special generation, but is only to be regarded as a part of the mother-plant 

 sexually influenced. The true alternation of generations of the Thallophytes con- 

 sists, according to Pringsheim, in the regular succession of independent so-called 

 neutral generations, having non-sexual propagation, and a single sexual generation. 

 Thus, zoospore-forming generations of Vaucheria, or j-Edogoniian, alternate with a 

 generation which bears the sexual organs. Both kinds of generations are of 

 essentially similar structure ; they are distinguished by the form of their propa- 

 gation. Only the first generation, which springs from the fertilised ovum, has often 

 properties which differ from those which follow, e.g. in Coleochcete. In the Mosses 

 this first non-sexual generation is much more sharply characterised; it is de- 

 veloped as the sporogonium, and is the only neutral generation ; it differs from the 

 sexual generation only by the scanty dcA'clopment of the vegetative part. 



While the views of Sachs on the one hand, and of Pringsheim on the other, 

 were showing some tendency to spread, other views appeared in opposition now to 



1898. 3 y 



