550 Prof. G. Klebs. Alterations in Developmeiit and [June 25, 



The third fundamental stage of development is the formation of sexual 

 organs. If we want to bring this about, the whole of the growing 

 fungus must be subjected to a slow decrease of its nutrition. Sexual 

 reproduction takes place much better when the external conditions at 

 the same time prevent the formation of asexual zoospores. Both stages 

 are, in every case, independent of one another, because they are controlled 

 by different conditions, and it is therefore possible to separate them. We attain 

 our object by cultivating the mycelium in a solution of leucin or haemoglobin 

 (heemaclirome), mixed with inorganic salts. After the quick growth of the 

 mycelium in the first four or five days, the quantity of nutritive substances 

 is diminished by degrees, and in consequence of this sexual organs appear 

 in great numbers. 



We can replace the sexual stage by the asexual one without difficulty, by 

 putting the mycelium with its oogonia into pure water, in which the ends of 

 the filaments bring the zoospores into existence. 



Sexual reproduction, itself a very complicated process, requires the 

 formation of male and female organs. -De Bary long since observed that with 

 some species of Saprolegnia egg-cells can mature witliout fertilisation by 

 male cells, and therefore represent a simple case of parthenogenesis. 



When the solutions of leucin or haemoglobin do not contain inorganic 

 salts, the mycelium produces exclusively female organs, of which the 

 unfertilised egg-cells become ripe spores. Formation of male organs — 

 and therewith fertilisation — takes place when salts, especially phospliates, 

 are added. It follows, from these facts, that the various stages of develop- 

 ment can be produced or prevented as we may desire, and also that the 

 succession (order) of tlie stages can be modified at will. 



The typical behaviour of the fungus on the dead insect is only one case 

 among many other potentialities, and is easy to understand from its 

 relation to the alterations of environment. The very strong growth of the 

 aycelium after settling on the insect, is the effect of highly nutritious 

 food. The filaments grow into the water, but in so doing they reach into 

 surroundings of poor nutrition, and must thereupon produce zoospores. 

 The nutritive substances contained in the insect are gradually consumed, 

 and tlio resulting general decrease of nourishment stimulates the fungus 

 into tlio foimation of sexual organs. After the complete exhaustion of 

 nourishment the death of tlie fungus (with the exception of tlie resting 

 Hj)()res) takes place. 



Numerous otlier lower jilants, such as fungi or alga>, show, in principle, tlie 

 same relations to environment, {jrovidcul that they can be well cultivated. In 

 all such cases we observe that the alteralronH of environment essential to 



