46 Natural History Bulletin. 



of the species are consequently of comparatively easy identifi- 

 cation to anyone possessed of a good microscope. 



Nos. I and 24 of the list subjoined are most interesting of all 

 because of the importance of the host-plants which they 

 affect. Phytophthora infestaus occurs on the potato and is the 

 fungus connected with the notorious "potato murrain" or "po- 

 tato disease" and so like many an other nuisance, has a place in 

 human history. The development of the fungus is favored by 

 sultry and w^et weather, alternating periods of fog and sunshine. 

 The climate of Iowa seems on the whole too dry. At all 

 events our potato crops have seldom been generally, or even 

 seriously affected, although the parasite is here. It is inter- 

 esting to note that the Tomato (member of the same family as 

 Potato) suffers a similar invasion from P. infcstans. 



No. 24 is, it would appear, more to be dreaded. In the 

 Government Report on the Fungus Diseases of the Grape \'ine 

 Mr. Scribner makes this statement: 



"The downy mildew {^P. viticola) is common to both the 

 wild and cultivated grapes of this countr}', and from the for- 

 mer it doubtless w' as conveyed to the latter in the earliest days 

 of American grape culture. In all the region east of the Mis- 

 sisippi, particularly in the central and middle Atlantic states it 

 has long been known as a serious pest. It is now reported 

 in California where the loss it occasions in some localities is 

 variously estimated at from ten to fifty per cent. In New 

 England and along the northern tier of states although of fre- 

 quent occurrence, its action is comparatively insignificant." 



In Iowa the native species suffer far more than those culti- 

 vated in vineyards although the latter are often affected. It 

 is not uncommon to see plants of Vitis rifaria white from top 

 almost to bottom with the downy mildew'. In vineyards it is 

 the old and neglected stocks only, whose enfeebled leaves turn 

 yellow and fall before the onset of the parasite. The fungus 

 Sometimes attacks the ripening fruit w^hen, of course, it attracts 

 general attention as entailing palpable damage and loss. 



