574 
Notes. 
a vegetative growth of whatever duration, or a continued propagation 
in one form, has never of inner necessity led to the appearance of 
another. 
We can now say that the majority of Algae and Fungi will behave 
like the species which have thus far been tested ; in which behaviour 
the relation of dependence of the propagation, on each occasion, 
upon the outer world will vary extremely according to the species. 
If one recognizes thus far as operative factors light, temperature, 
moisture, oxygen, chemical composition of the nutritive medium, here 
is already at hand a great wealth of most various combinations of 
external stimuli which set the formative processes in motion. Further 
investigation will teach what a wealth of unexpected relations is here 
to be discovered between the outer world and organic life. 
Despite all this, the possibility remains that in certain species a 
regular alternation of neutral and sexual generations does appear. 
That might be possible for the Florideae, in which the tetraspores and 
carpospores are often formed on special individuals. This simple 
fact proves nothing as yet, since it is faced by the other fact, that 
both kinds of propagation also appear from the like individual. The 
question remains open whether the tetraspores do not make their 
appearance at times, and seemingly on individuals other than do 
the carpospores, for the simple reason that the external conditions for 
the two of them are very dissimilar. The question cannot be decided 
till longer-continued cultures of the Florideae have been arranged. 
The answer will presumably not turn out differently from that in the 
case of other Algae. At the first glance an alternation of generations 
in Pringsheim’s sense comes to much clearer expression in certain 
parasitic Fungi, especially in the Uredineae. If we leave aside the 
undecided question as to the occurrence of a sexual act, the observa- 
tions and experiments teach that the life of a Fungus such as Puccinia 
graminis necessarily takes the course of the alternation of two inde- 
pendent generations living upon different host-plants, the one bearing 
teleutospores, the other forming aecidia. In addition there are still 
the subsidiary fruit-formations of the uredospores and of the spermo- 
gonia. In fact we have here a regular alternation of generations, 
such as appears in analogous form in the case of several of the lower 
animals; there is no obvious reason for avoiding the expression in 
this case, if one takes into account the actual circumstances of the 
case. But still it would be wrong to apprehend this alternation of 
