BRIEFER ARTICLES 
DWARFING EFFECT OF TREES UPON NEIGHBORING 
PLANTS 
The unfavorable effect of trees upon the growth of most plants 
rooted in the soil immediately about them is generally attributed to one 
or all of the following influences: (1) undue shade; (2) withdrawal 
of moisture from soil by the tree roots; (3) withdrawal of nutrient salts 
by the tree roots; (4) possible excretion of injurious substances into the 
soil by the tree roots. 
Every observing farmer is well aware of the injury to most crake 
caused by the proximity of tree belts, hedges, or even of single large 
trees, and the loss caused in this way by trees is often considerable. 
Undoubtedly partial exclusion of light is an important factor. Cases 
in which fruit fails to mature may often depend upon this. The writer 
has found that the black raspberry (Rubus occidentalis) grew and flowered 
freely but failed to ripen fruit in a situation in which the bushes during 
the earlier half of the day received only one-twelfth to one-fifteenth of 
the total sunlight, although they were hardly at all shaded during the 
afternoon. 
The present very rainy summer (1915) has afforded a suggestion as 
to the importance of the second of the factors previously mentioned, the 
withdrawal of moisture, in dwarfing plants growing under trees. The 
average rainfall in Boston for July is about 3.24 inches. This year the 
amount for July was in Boston 8.85 inches and in Cambridge 10.34 
inches. The Boston record much exceeds that of any July precipitation 
during the 44 years for which the Weather Bureau has published a 
climatological summary of its observations.* 
uring the month of July of the present year the writer noticed 
that several species of perennial mesophytes which grew just north of 
and shaded by a belt of deciduous trees (wild cherries, ashes, and maples) 
were reaching unusual dimensions. Three most notable instances were 
« No doubt the Cambridge rainfall for July of the’ present year is also the maximum 
for a long period. There is no readily accessible summary of total rainfall in Cam- 
bridge, month by month. 
491] [Botanical Gazette, vol. 60 
