570 
Notes. 
ALTERNATION OF GENERATIONS IN THE THALLO 
PHYTES. — Since the pioneering investigations of Hofmeister, it has 
been generally recognized in Botany that the Archegoniatae are 
characterized by a definite form of alternation 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 
the spores-^the sporophyte. An essential difference separates the 
two divisions of the Archegoniatae. In the Pteridophyta the game- 
tophyte 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 sporophyte is repre- 
sented 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 Archegoniatae, 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 
characterized generations is to be observed; and secondly, what in 
that case is the connexion between this alternation, should it turn 
out to be a fact, with that of the Archegoniatae. 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 
(1874), who there endeavoured to make the course of development 
of Algae and Fungi fit with that which holds in the Mosses. The 
life of Vaucheria , Mucor , an Ascomycete, or one of the Florideae, 
is divided according to Sachs into two sharply separated parts, of 
which one is characterized by the appearance of sexual organs, the 
other by the spore-bearing tissue which springs from the fertilized 
ovum. Thus the mycelium of a Mucor which bears the sexual 
organs, the thallus of Vaucheria , or of the Florideae, represent what 
we now term the gametophyte ; the fruit-body of Ascomycetes or 
of Florideae, the zygospore of Mucor , the oospore of Vaucheria , 
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 Archegoniatae. The 
