508 State Board of Agriculture, &c. 



action of that fungus upon these tissues, announced the true 

 cause of the potato rot. The newly discovered fungus, 

 from its affinity with other previously known forms, was 

 pronounced a Peronos;pora, and received the specific 

 name of infestans. 



The organs of vegetation of the fung'^us were, by aid of 

 the microscope, traced through the tissues of leaf, stem, and 

 tuber. These consist, in general with fungi, of elongated 

 cells, placed end to end, and forming continuous threads, 

 more slender than gossamer, and woven together into a 

 loose network, which runs through the whole structure of 

 the infested plant. This network receives the name of 

 nnyceliu7n, or spacon^ and performs the functions of both 

 stem and roots. It lives and grows at the expense of the 

 assimilated material of the plant upon which it preys. 



The organs of reproduction of the new Peronospora 

 were also observed and described, — those, at least, which 

 are now known to constitute the simplest mode of repro- 

 duction. These organs are slender threads, as thin as the 

 threads of the mycelium, which branch from tlie mycelium, 

 rise usually above the surface of the leaf through its breath- 

 ing pores, speedily branch in different directions, and finally 

 bear fruit on the tips of their branches. These fruits are 

 usually termed simple spores, or, in technical language, 

 conidia, because from their smallness they are dust-like. 

 They are so minute as to be individually imperceptible, 

 and so numerous that it is difficult to conceive a space that 

 may not contain them. These bodies at maturity detach 

 themselves from the mother plant, and being dispersed in 

 the ail' fall back upon the potato plant, or are borne to oth- 



