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closely observed, little thickenings and buds will be observed 

 in the mycelia themselves as apart from conidiophores. 

 These thickenings and buds are called Oogonia and the 

 enclosed cells Oospheres. Smaller buds growing out of 

 the mycelia will be also noticed which are called the 

 Antheridia. The Antheridia are the male cells and these 

 coming in contact with Oogonia, and the protoplasm of the 

 Antheridia flowing into the Oospheres, fertilisation takes 

 place and Oospores are the result. These fertilised Oospores 

 are also called Resting Spores. They are round and some- 

 times smooth and sometimes spiney in appearance looked 

 at under a powerful microscope. The Oospores abound in 

 diseased seed-potatoes after they have germinated and spent 

 themselves. The perennial mycelium in the tuber, not being 

 able to produce conidiophores and conidia (which require 

 contact with free atmosphere for their development), deve- 

 lops oogonia and antheridia as it multiplies. As zoospores 

 give rise to germinal threads so do oospores when kept 

 uniformly moist and warm. The oospores are of brown 

 colour and thus easily distinguished from zoospores, which 

 are almost colourless. The oospores, having a longer vitality 

 than zoospores, and remaining in old potato fields in decayed 

 tubers and old leaves and haulms, they germinate again next 

 summer and it is usually by their means and not by means 

 of the perennial myclia of the seed-tuber, that potato disease 

 reappears year after year. As the potato-disease spreads 

 from leaf to stem and from stem to tuber and as it is never 

 observed to take the opposite course of development from the 

 tuber upwards, the source of infection is not so much the seed- 

 tuber as the decayed haulms and tubers of the previous year. 

 It is not necessary for the mycilial growth from the oospore 

 to take place on the leaf of the potato plant itself. The 

 fungus can grow at first on the moist soil and then gradually 

 spread by means of conidia and zoospores to the leaves of 

 the new crop. The source of infection being chiefly the 



