1898.] PUBLIC DOCUMENT — No. 33. 49 



with two gases, hydrocyanic and formaldehyde. Neither 

 of these appears to answer the purpose. The former, which 

 has been found to be of considerable value as an insecticide, 

 cannot be made effective as a funs^icide without using; a 

 strength which will prove fatal to the plant. This we have 

 determined by parallel exposures of various fungous spores 

 and plants to the gas, and also by the fact that spores of the 

 carnation rust, taken from plants which had been almost 

 killed by over-exposure, germinated freely. Formaldehyde 

 has a well-marked fungicidal effect, and is much less harm- 

 ful to plants ; but we cannot at present recommend it as a 

 general fungicide, on account of the difficulty of producing 

 it in sufficient strength. 



The past year has been an exceedingly abnormal one for 

 vegetation, and as a result this division has had many in- 

 quiries concerning plant diseases, different from those of 

 ordinary years. The excessive and long-protracted rains 

 and the lack of sunshine gave rise to a multiplicity of plant 

 diseases such as we have not had for some years. This was 

 the case not only in regard to our various crop plants, but 

 our introduced ornamental species and even our wild plants 

 were unusually affected by fungi. An unusual number of 

 the so-called spot diseases made their appearance, and de- 

 foliated to a greater or less extent more than one species of 

 tree. These spot diseases were especially disastrous to the 

 sycamore and butternut, both of which in many instances 

 lost all their foliage ; while other trees, such as the chest- 

 nut and wild cherry, were more or less affected. The fungi 

 causing these diseases are not new to these trees in this 

 locality, but the abnormal conditions to which all vegetation 

 was subjected proved amply sufficient to accelerate their 

 growth and development. 



Whenever the normal conditions surrounding the plant 

 are disturbed, we must expect to find irregularities in its 

 functions ; and any serious irregularities in the plant's func- 

 tions are most likely to manifest themselves by the presence 

 of some insect, fungous or bacterial organism. Abnormal 

 functions, or, in other words, physiological disorders, are 

 in a majority of jnstauces the basis of many plant disease!? 



