INJURIOUS AND OTHER FUNGI. 39 



The potato rot has long been known to the South American In- 

 dians dwelhng in the regions of the Andes, showing that this plague 

 is not of recent origin, and also that the land which gave us the wild 

 potato has hkewise produced its most destructive parasite, which 

 has followed it across the seas. There is no object in nature con- 

 cerning which men have given more cmious and conflicting theories 

 than the plant in question, and to-day the list is long of those who 

 fail to recognize in it a member of the vegetable kingdom. But 

 when the plant can be cultivated, the spores sown on sound pota- 

 toes, and the vegetable watched through its whole existence, culmi- 

 nating in the rot, it is time to believe that it is as much a plant as 

 the one upon which it grows. 



Another species of this same genus, Peronospora^ is the Ameri- 

 can Grape-^due Mildew. The true grape disease, the one which 

 has proved so disastrous at different times to the vines of Europe 

 and Madeira, is caused by another fungus, to which Berkeley has 

 given the name of O'idium Tuckeri. It is a form of a fungus which 

 has not been recognized in its perfect state, and is supposed to oc- 

 cur to some extent on this side of the waters ; but as many species 

 have this conidial form, and some nearl}' identical with it, and also 

 growing on the gTape, there may be some doubt as to our vines ever 

 being attacked by the true grape disease of Europe. The Perono- 

 S2)ora viticola, the mildew which most interests the grape growers 

 of America, is quite common, appearing on the under surface of the 

 leaves about the first of August, and continuing to flourish until the 

 leaves will nomish it no longer. It can be most easily seen on the 

 smooth leaves of the Vitis cordifolia, having the appearance of 

 small, frost-like spots, which rapidly spread and soon cover the 

 whole leaf, frequently extending down the petiole to the stem. 

 This fungus, lilie the potato rot and other closel^'-related species, 

 flourishes best in moist, warm weather. Under the microscope, the 

 tissue of the grape leaf is seen to contain an abundance of minute 

 threads, which force their way in all directions between the cells of 

 the leaf, tlirusting their suckers into the cells to rob them of then- 

 nourishment. When the time for fruiting comes, the threads pass 

 out of the stomata of the leaf and branch in a definite manner, and 

 bear the asexual spores on their tips, as we have observed in the 

 potato rot. Under the head of the germination of these asexual 

 bodies, Dr. Farlow has performed some interesting experiments. He 

 finds they germinate equally well in the dark as in the light. Those 



