xxxv.] POTATO DISEASE, I. ITS ACTIVE STATE. 293 



and many other fungi may exist in inconceivably small 

 and perhaps Amoeboid particles. 



The resting of the mycelium in a state of hibernation 

 through the winter may, perhaps, sometimes account for 

 the reappearance of the disease the next season ; for it has 

 been known, since Mr. Berkeley pointed it out in 1846, 

 that a broken or cut surface of a diseased potato will, if 

 the mycelium is alive, give rise to the potato fungus at 

 any time of the year on the cut potato being exposed to 

 an atmosphere suitably warm and moist. It is obvious 

 that, if the potato disease is annually reproduced by dis- 

 eased tubers containing perennial mycelium, the disease 

 must invariably begin in the seed-tuber and ascend the 

 stem ; but it is known by experience that in the vast 

 majority of instances this is not the case, but that the 

 disease first invades the leaves. 



Flowering plants have three familiar modes of increase. 

 One is by suckers, runners, or underground stems ; these 

 runners are roughly comparable with perennial mycelium. 

 A second is by buds or bulbils, at times very common in 

 the axils of the leaves of some lilies ; these may be com- 

 pared with the conidia or bud spores of fungi; and a third 

 is by the reproductive organs, or stamens and pistil. 

 ^Reproductive organs of a like nature, as far as sex is con- 

 cerned, are known in fungi, and they are potential to and 

 extremely common, well marked, and easily seen in the 

 genus Peronospora, to which the potato fungus belongs. 



The organs belonging to Peronospora infestans, Mont., 

 as far as we have at present described them, have been 

 distinctly asexual, or without sex; no male and female 

 organs answering to the stamens and pistils of flowering 

 plants have yet been referred to. 



Mr. Berkeley as long ago as 1846 described and illus- 

 trated, from materials furnished to him by Dr. Montagne, 

 what he believed to be an oogonium, an organism which 

 may be compared with an ovule or unimpregnated egg, and 

 its oospore, or resting-spore condition, which is more or less 



