EXPEEIMENT STATJON HKl'Oirr. r,l9 



most diligent scaivli I havo failed lo tiiid tlie h'ast sign of the '•winUT 

 fruit." If one should ask for the liistory of the species here repre- 

 sented in tlie rapidly-spreading summer form, no positive answer 

 could be given. There is a species {Mi^crospluvra Moitgeotii I^ev.) 

 upon the same host that is as yet recorded only for P^urope. It is 

 seen that it is the reversed case of the Oidhun Tuckeri, above men- 

 tioned, and it remains to find the "winter fruit," or, failing in this, 

 to call it by the name of the last species mentioned, with a question 

 mark added, or name it Oidmm Lycii tentatively. 



The classification of the species, as previously stated, is founded 

 chiefly upon the peritheeia, their appendages and contents. First, cer- 

 tiiin species, along with other characteristics, have but one spore sac in 

 the penthicium, thus making two primary groups of the mildews. 

 Second, the appendages are unbranched, branched, sharp-pointed or 

 with curved tips. By means of these few characters the species are 

 separated into six genera, as shown by the following key. 



Spore sac in penthicium one — 



Appendages, branched Podosphcera. 



Appendages, unbranched Sphcerotheca. 



Spore sacs in penthicium more than one — 



Appendages, curved TJncinxda. 



Appendages, branched Microsphcera. 



Appendages, unbranched Erysiphe. 



Appendages, needle-shaped. Phyllactinia. 



These six genera are represented in the United States by the fol- 

 lowing number of species: 



Species. Varieties. 



Poilosphcera 3 and 1 



Sphcerotheca 5 '' 1 



Uncinula 9 



Microsphcera 5 and 4 



Erysphe 6 



Phylladinia 1 



Total 29 6 



After the genus has been determined, which is a very easy matter 

 as a general rule, another set of characters is considered, and here the 

 greatest care is required. Let us take the mildew of the lilac for a 

 consideration of the specific marks. For these a compound micro- 



