PLANTING AND CARE OF TREES 19 



ing of snow, however, may offer as good a background as the sky 

 and allow a tree to be photographed against a hillside where other- 

 wise a satisfactory photograph would not be possible (p. 357). A 

 white sheet held behind the trunk may afford an artificial back- 

 ground for a bark photograph. Generally this is not 

 necessary since bark photograi^hs are taken at close range 

 and the surrounding objects are mostly out of focus. 

 If need be, the background can be painted out on the 

 negative. For habit pictures in sunlight we have found a No. 

 16 stop and 1/25 — 1/20 second exposure to give good results when 

 the wind will allow so long an exposure. For bark pictures the 

 smallest stop and a proportionately longer exposure, say 1/2 to 1 

 second, will give the greater detail desired in such pictures. 



To one interested in botany as an avocation, trees furnish an 

 especially available subject for outdoor study. They are acces- 

 sible in city or in country, in winter or in summer. Their size 

 renders them conspicuous. They can accordingly be studied from 

 a carriage, an automobile, or a rapidly moving train, and in this 

 way much learned that would be impossible to discover if the study 

 were confined to a single locality or if the student were dealing 

 with smaller forms. 



Tree Ecology — Ecology, the study of plants in relation to 

 their environment, finds in trees a most convenient group in 

 which to carry on investigations. The subject is comparatively 

 new and many problems are as yet unsolved. After some familiarity 

 has been gained with the trees that grow in one's own locality, it 

 will be possible to discover something about their distribution. A 

 list of the local tree flora of one's state, county or town or even of 

 a more restricted area has a distinct value if carefully made, but it 

 is far from being the end of tree study. What trees are usually 

 found growing together and what are the causes that bring them 

 to be thus associated? Is there a swamp "association," a dry hill- 

 side association or other associations of more or less well marked 

 character? What is the influence exerted upon the various species 

 by differences in character of the soil and its chemical composition 

 — the presence or absence of lime for example — the amount of 

 available moisture, the altitude, the exposure to the sun and wind 

 on different sides of a hill or mountain, the climate and other such 



