240 AGRICULTURAL EXPERIMENT STATION. [Jan. 



and indeed doing its chief harm in rendering the former 

 insipid and worthless. I have not seen it on tlie fruits, but 

 it may be likely to be found upon them, and in this aspect 

 the fungus may assume, under favoring conditions, consider- 

 able economic importance. Suggestions as to treatment 

 may be found on subsequent pages. 



2. The Powdery Mildew of the Gooseberry (Sphce- 

 rotheca mors-uvoe (Sz.) B. & C.) (PL III.) was received, 

 last summer, from W. C. Strong, Esq., ofWaban, on the 

 leaves, twigs and berries of the " Triomphe " gooseberry, a 

 variety which has been claimed to be mildew-proof. In the 

 present case the utter groundlessness of such a claim was 

 strikingly shown, and aflbrded further evidence that we are 

 safe only in speaking of varieties as more or less liable to 

 the attacks of fungous diseases. It is not probal)le that any 

 of our horticultural varieties are in any absolute sense 

 disease-proof, and it may fairly be doubted if we shall ever 

 originate such, without sacrifice of more essential features, 

 even with constantly increasing understanding of the requi- 

 site qualities. 



This fungus is very closely related to that last described, 

 and differs from it only in very unimportant particulars. 

 The mycelium forms a dense felt over the infected parts of 

 the host-plant, and in the early part of the season is nearly 

 colorless, and produces the " Oi(/a«w " form in abundance. 

 Later, the mycelium becomes quite dark-colored, and gives 

 rise to the perfect spore form (figs. 23, 24). As above 

 indicated, all the younger, succulent parts of the jolant may 

 be involved, and thus not only is the season's fruit destroyed, 

 but the normal production of new wood and preparation for 

 another season is prevented. This gives to the fungus 

 great economic importance, especially since it is widely dis- 

 tributed. It has been frecjuently mentioned by writers on 

 plant diseases, and the accounts by Arthur * and Halsted f 

 may be consulted for further information. Notes on the 

 treatment of this class of diseases are given later. 



* Sixth Report New York Experiment Station, p. 349, 1888. 

 t Mycological Report, United States Department Agriculture, 1887, p. 373, with 

 plate. 



