1897-98-] Plants which dissipate Energy. 393 



learned something. We wanted to get the very commonest 

 of moulds, one known to every gardener, the cause of the 

 damping-off of seedlings ; and we sowed cress in the orthodox 

 fashion and kept it closely covered with a bell-jar, and the 

 moisture hung like dew for weeks on the little plants, but no 

 fungus appeared. We repeated this, and I looked through 

 several greenhouses and could find no damping-off; evidently 

 there were few Pythium spores in the air here last winter. 

 Then we wanted to get zygospores, and we put bread and jam 

 in covered moist dishes : we got plenty of mould, but no 

 conjugation. We consulted our books. One distinguished 

 author explained the matter so far : he said that conjugation 

 takes place at the end of summer only. Zygospores are 

 furnished with a thick coat, which can long withstand the 

 inclement season. That seemed a satisfactory explanation. 

 What was much more interesting was, that by following 

 Klebs' recent researches conjugation could be brought about 

 at will. Moulds can be made to reproduce themselves 

 vegetatively or sexually by keeping them at different tempera- 

 tures. When moulds are grown about 28° C, zygospores 

 appear in a very short time. This physiological effect of 

 a considerable rise of temperature is of great interest. It has 

 a parallel amongst the green algse. Take a handful of the 

 tiny green threads which grow in every clean pond or in the 

 ditch at the side of every country road. You will probably 

 find amongst them Spirogyras or Vaucherias in abundance. 

 When in their native home they will most likely be growing 

 vigorously — they will be in a simply vegetative condition ; they 

 have abundance of air and sunshine, and are kept in continual 

 gentle agitation. Place them in an aquarium or a tumbler 

 (preferably at a north window) ; they will continue to grow, 

 but the conditions are changed. They are no longer in 

 a cool, well-aired stream, carrying a good deal of carbonic 

 acid and mineral matter ; they have been transferred to 

 a stagnant pool, fanned by no breezes and subject to great 

 changes of temperature, and as the conditions are the same 

 all through our vase, an epidemic of conjugation takes place. 

 These are illustrations of how change in the environment acts 

 immediately on the organism. 



In studying the lower fungi — the moulds — we cannot but 



