47 



cle entitled "Combating Aphis on Violets," published by Mr. Gallo- 

 way in American Gardening for November 6, 1897 (Vol. XVIII, 

 p. 758), from which the following is quoted: 



Aphides, especially the black ones, were once the most serious pests with which we 

 had to contend. Since we have adopted the hydrocyanic-acid gas treatment, how- 

 ever, * * * we have had no serious trouble. So important do we consider this 

 matter of being able to use this gas that we shall plant in the future throughout the 

 entire season in such a way that the plants may be fumigated at any time. 



We abandoned tobacco entirely some time ago, as we found by experience that, 

 no matter how used, it would tend to weaken the foliage and make it more subject 

 not only to ' ' spot, ' ' but to other diseases as well. * * * When tobacco is used, 

 either as smoke, dust, stems, or extract, it seems to in a measure check the vital 

 functions of the leaf, the little cells of which temporarily lose their vitality and 

 their ability to resist outside influences. Here is the opportunity the fungus needs, 

 and it at once takes advantage of it by sending a thin, thread-like growth into the 

 cells. Once the tissue is entered, the fungus continues to grow until the plant is 

 able to check it of its own accord. The spot then turns white, but when conditions 

 are again favorable the fungus will start anew, and the spot will be found soft, 

 greenish, and watery, etc. 



THE VIOLET "GALL FLY." 



(Diplosis violicola Coq. ) 



Violets and roses are subject to the attack of different forms of 

 minute larvae or maggots, the young of what are known to florists as 

 gall flies — minute two-winged flies or gnats of the family Cecidomyiidae. 

 Three species are of importance as enemies of these plants, and there 

 are doubtless others, but these three are the only ones that have 

 obtained marked recognition by their injuries in recent years; until 

 recently, indeed, they were not recognized as distinct from others of 

 their kind. They have been given more or less study by the writer 

 and by some others, and, when it was made manifest that they were 

 undescrrbed through special study by Mr. D. W. Coquillett, of this 

 office, all of the notes and manuscripts which had accumulated at that 

 time were turned over to him, and the results were embodied in two 

 somewhat technical articles, with full descriptions, in Bulletin No. 22 

 of the present series. 



DESCRIPTION. 



The larva or maggot, which is usually found folded up in the leaf 

 of a violet in such a manner as to bring the upper surfaces together in 

 what has been termed a gall, is a minute, legless creature of a whitish 

 or yellowish color. The general appearance of one of these larvae is 

 shown in figure 16 at d, e representing its breastbone. 



The parent gall fly is a minute, slender and delicate two-winged fly, 

 measuring about one-twentieth of an inch in length. It has long and 

 slender legs and antennae, the latter 14-jointed and surrounded by two 

 whorls of bristly hairs on joints 3 to 13, inclusive. 



