1910.] Forms of Plants as a Result of Environment. 549 



the so-called oogonia, which contain at least two and sometimes many more 

 egg-cells, the oospheres. Upon other filaments branches arise, which grow 

 into the oogonia and, pressing against them, produce the male antheridia. By 

 means of a penetrating tube a part of the male fertilises the egg-cells, which 

 turn into spores, germinating after some months of rest. The fungus itself 

 dies after a few weeks of development. 



The question is whether this very regular succession of the different stages, 

 each with its special forms and functions, is really dependent on internal 

 causes. If we want to recognise the conditions of this development, we must 

 first know as exactly as possible the conditions of life, especially the manner 

 of nutrition. The fungus is easy to cultivate either on a solid or in a liquid 

 medium, which must contain principally nitrogenous substances, such as 

 albumen, peptone, extract of peas, etc. In such very favourable solu- 

 tions only vegetative growth of the mycelium takes place. When we take 

 care to keep up the good nutrition by putting a piece of the mycelium into 

 fresh food solution from time to time, it continues to grow without inter- 

 ruption, and can never reach any other stage of development, for instance, 

 the asexual or the sexual reproduction. I devoted six years to carrying out 

 this experiment. 



We can just as little imagine that under constant external conditions the 

 fungus reproduces by itself an alteration of its development, as that water 

 l^ecomes ice by itself under constant temperature and pressure. Therefore, 

 under such constant environment the fungus must be really immortal. Each 

 stage in its development requires an alteration of the external conditions, and 

 the genesis of its reproduction is the beginning of its death. 



The second stage of development, the formation of asexual zoospores, can 

 ^easily be caused by putting a piece of the fungus from the food solution 

 into pure water. Innumerable zoospores come into existence during the 

 next few days, till the mycelium finally dies. The speed of formation depends 

 on the temperature ; at 1 degree it is finished in 48 hours, at 20 degrees 

 in eight hours. The essential cause of the process is the decrease of 

 nutritive substances in immediate proximity to the ends of the filaments. 

 To cause the formation of zoospores it suffices, for instance, to put the 

 fungus from a solution containing 0-01 per cent, of peptone into one containing 

 O-OOl per cent. We can effect the continuance of the formation of zoospores 

 for a long time by cultivating the fungus on solid white of egg, and keeping 

 it in water, which must be changed from time to time. The filaments, being 

 well nourished, grow into the but slightly nutritive water and continue to 

 •develop zoospores there as long as the substratum affords the necessary 

 nourishment. 



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