EEPORT OF THE BOTANIST. 81 



produced by a peculiar sexual process. These late spores are incased 

 in firm covering, ot peritJiecia, that serves to protect them from the exi- 

 .ij^eucies of the winter season. Before the connection between these 

 vo fruitiug forms had been determined the first was classified in a dis- 

 ;ii:ct group, designated under the generic name of Oidmm. The early 

 stage of the white mildew, often so injurious to our grape-vines, has been 

 described as Oidium tuckeri, a species which has seriously ravaged the 

 Aineyards of Europe. Whether the Oidium of this country is the same 

 as that of Europe has not been proven, but Dr. Farlow has shown that 

 the so-called " Oidium tuckeri " of this country is only the summer or 

 couidial state of a species of JJncinuIa* {U. sj>iraUs). 



Oidium leiicoconium bears a similar relation to the well-known "rose 

 mildew" and ^^ goosebevrj hlight'' {SpJiccrotlicca parmosa). In point of 

 iujury occasioned, this species is quite as injurious as the JJncinuIa of 

 the grape-vine. It is a serious enemy to rose culture ; it is reported as 

 common on the peach in California and upon the cultivated raspberries 

 in Iowa. From widely distant localities it is reported as doing much 

 damage to the gooseberry, attacking not only the leaves but the fruit 

 as well. Wo have received gooseberries from Utah almost wholly en- 

 veloped in the brownish felt-like growth of the mycelium of this fungus. 

 Other species of this group i)rey upon the leaves of the cherry and ap- 

 ple or upon the foliage of various forest trees. One produces the white 

 mildew, so common late in the season on the leaves of the lilac, another 

 is injurious to the late-grown peas. It is needless at this time to fur- 

 ther extend the list. 



Tlie specific for white mildews is the flowers of sulphur, and if used when the fungi 

 first make their appearance, it will stay tl.eir ravages. This remedy is best applied 

 with a bellows and when the aliected plants aro wet with dew or rain. The sexual 

 'spores are so well i^rotected that when once formed they require a more violent rem- 

 edy. The summer spores are naked and thin-walled and aro easily reached by sul- 

 phur. The incased spores of late autumn, designed to carry the species over the 

 winter, and the natural exposure of the leaves to moisture and frost, only prepare the 

 perithecia for the escape of the spores. The placing of the infested parts in a com- 

 post heap would only aid in the preservation and distribution of the spores. The 

 best method is to bum all mildewed parts of the i^lants and thus bring au end.t 



Unlike most fungi, hot, dry weather appears to favor the development 

 of the white mildew. 



Many of the diseases of our fruit orchards might be remedied, or at 

 least diminished, by raking together and burning tbe leaves as soon as 

 they have all fallen. ATithin the substance of the leaves the spores 

 of a number of injurious fungi are supposed or known to iiibernate. 

 Above all, these leaves should not be used as material for compost, for 

 it is probable that this would only serve the better to preserve the vi- 

 tality of the spores through the winter. The plan of raking \\j) the 

 leaves and burning them has been especially recommended as a means 

 of checking the growth of the apple-scab fungus and the pear-tree 

 scab. In respect to the latter disease, it is not confined to the leaves 

 and fruit, but extends to the young shoots also. When the shoots are 

 afiected they must be removed, with the knife and destroyed along with 

 tbe leaves. Great care must be taken in selecting grafts. They should 

 never be taken from trees diseased with the scab, as it has been proven 

 that the disease can in this way be transferred. 



If this disease be taken early, say at the time of the formation of the 

 conidial or summer spores (the only spores so far known), the direct 



* Farlow in EulL. Bussey lust. 



tDr. Halsted, in Proceedings American Pomological Society, 1883. 



G AG— '85 



