TRANSACTIONS OF SECTION K 1059 



realised in opeu nature, aa well as in the laboratory. In particular, the sexual 

 propagation is often dependent upon more complex conditions than the non-sexual. 

 While both can be induced without difficulty in Sporodinia, in other Mucorini it 

 is most difficult to see the zygospores at all. I have not succeeded in my attempts 

 to induce the formation of zygospores in the common and easily cultivated Mucor 

 racemoms, though such formation doubtless exists. 



In the works of Brefeld the idea is often expressed and tested, of brino-ing a 

 Fungus by culture through the most numerous successive conidium-forming genera- 

 tions to its higher fruit-form. This idea is connected with Brefeld's idea that 

 inner causes are more important than external causes for the appearance of the 

 fruit-form. The result of the serial-cultures of Brefeld, whether positive or neo-a- 

 tive, was under all circumstances accidental. The experiments would prove the 

 view of Brefeld only if the external conditions had really been always the same 

 in all the numerous serial cultures. Since Brefeld, to judge from the meaore 

 statements of his methods of culture, has not paid any attention to this constancy 

 of the conditions, it will also have been a matter of chance whether they remained 

 the same, or varied in such a way that another form of fruit took the place of that 

 which preceded it. In any case, I may assert that if in Fungi such as Sporodinia, 

 Saprolefftna, Ascoidea, Eurotium, those external conditions are maintained con- 

 stantly which are characteristic for one of the forms of propagation, that same 

 form only is produced. Hitherto a vegetative growth of whatever duration, or a 

 continued propagation in one form, has never of inner necessity led to the appear- 

 ance of another. 



We can now say that the majority of Algre 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 recognises 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 alterna- 

 tion of neutral and sexual generations does appear. That might be possible for 

 the Floridese, 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 FlorideiB have been 

 arranged. The answer will presumably not turn out differently from that in the 

 case of other Alg;To. At the first glance an alternation of generations in Prings- 

 heim's sense comes to much clearer expression in certain parasitic Fungi, especially 

 in the Uredineic. If we leave aside the undecided question as to the occurrence of 

 a sexual act, the observations and experiments teach that the life of a Fungus such 

 as Pucci)iia f/rmninis necessarily takes the course of the alternation of two inde- 

 pendent generations living upon different host plants, the one bearing teleutospores, 

 the other forming ;ecidia. In addition there are still the subsidiary fruit forma- 

 tions of the uredospores and of the spermogonia. 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 generations as if we had here an 

 essentially new process, as against those other sorts of Fungi which are dimorphic 

 or polymorphic. There are nearly allied Uredineae in which all the spore forms 

 appear one after another upon the same mycelium. In my view the condition for 

 the different kinds of propagation will also be unlike, and the regular alternation 

 of the fruit forma would be explained by the fact that by the development of the 



3T2 



