BROAD-LEAVED EVERGREENS 341 



preparation of authentic lists of species on this basis will 

 necessarily be a slow procedure, the outcome of careful experi- 

 mentation, but fortunately a general though not infallible 

 guide to the need of soil acidity for a particular species is 

 already in existence in such well-known works on gardening as 

 Nicholson's Illustrated Dictionary of Gardening and Bailey's 

 Standard Cyclopedia of Horticulture. European gardeners 

 have learned from long and cumulative experience that certain 

 plants thrive best when supplied with peat, and this knowledge 

 has been handed down to us in garden literature, and in garden 

 practice when conducted intelligently, but never apparently 

 with any suggestion that the essential quality of the peat is 

 its acidity. The statement in any reliable work on gardening 

 that a particular species requires peat may be taken as good 

 evidence that this is an acid-soil plant. In very many cases, 

 however, especially in American works, this evidence is lacking. 



DISEASES AND INJURIES OF ORNAIVIENTAL BROAD-LEAVED 

 EVERGREENS.— Dickson 



Winter-injury. 



In cold winters, broad-leaved evergreens may be more or 

 less severely injured, especially when growing in exposed 

 situations. The injury is very similar to the winter-killing of 

 conifers and takes the form of a burning of the foliage and 

 killing-back of the young branches. In severe cases the whole 

 plant may be killed. The plants may appear normal until 

 early in the spring when, under the influence of the warm 

 winds, they turn brown within a few days. The Japanese holly 

 (Ilex crenata) and rhododendrons, especially R. maximum and 

 R. catawbiense, have shown themselves much less susceptible 

 to this type of injury. The exact cause of the injury is not 

 definitely known, but it is probable that it is partly due to 



