572 
Notes. 
(1890), and put on a footing of detail. Bower holds that the antithetic 
alternation came about by the intercalation of the non-sexual genera- 
tion, the sporophyte, as a quite new development between two 
gametophytes. This interpolation of a special sporophyte probably 
took place in the alga-like ancestors of the Archegoniatae, as they 
passed from a life in water to a life upon the land. In the series 
of the Thallophytes there are, in addition to the homologous alternation 
of generations, more or less advanced beginnings of an antithetic 
alternation, as for instance in Coleochaete , the Ascomycetes, and 
Florideae. 
All these various conceptions of alternation of generations in the 
Thallophytes rest on morphological comparison of the hitherto 
known facts of the life-history, while still very little was known of 
the behaviour of these organisms in open nature, or in long-continued 
cultures. Yet by such observations only is it possible to decide 
whether an alternation of generations can be proved at all, and how 
the influence of the outer world, so often assumed, really affects 
the course of life of the Thallophytes. These questions were the 
point of departure for my investigations on the conditions of pro- 
pagation in Thallophytes. The investigation had to be extended 
in two directions : in the first place, it was necessary to decide 
whether there is a regular alternation of free and independent 
generations ; secondly, whether a non-sexual generation characterized 
by special qualities arises of inner necessity from the fertilized ovum. 
The first question receives its answer, according to the results 
of my investigations, that no regular alternation of neutral and 
sexual generations exists in any of the Thallophytes which have 
been tested. They possess two or several kinds of propagation, 
each of which is directly dependent upon quite definite external 
conditions. If we take any vegetative stage we please, a filament 
of a Vaucheria , an Oedogonium, a piece of mycelium of a Sporodinia 
or Ascozdea, there are then present in each part the specific potentialities 
of sexual and non-sexual propagation. In open nature the fortuitous 
conditions determine which of the potentialities is developed, and 
how the modes of propagation follow one another, whether upon 
the same individual, or on different individuals. An exact knowledge 
of the conditions gives the experimenter the secure control over the 
organism, which can at will be forced into any desired mode of 
propagation within the limits of its species. The problem becomes 
