THE AMERICAN BOTANIST. 
porlance, and closely allied to temperature. It is usually deter- 
mined by the inverse method, observations of clouds and cloudi- 
ness, rather than the actual sunshine, although of late years many 
of our stations are equipped with sunshine recorders, and the ap- 
proximate hours of sunshine are obtained with a fair degree of ac- 
curacy. 
The effect of sunshine in determining the form of plants is w^ell 
known. If a plant germinate beneath a box, board, or stone it 
does not spread out at random, but takes the shortest path to the 
sunlight, where it spreads out in its usual form. The form and 
direction of growth of every branch, leaf, or shoot of a plant is 
controlled largely by its accessibility to the light. This is true 
even to the development of the branches, for these bud and grow 
where the leaves can unfold to the light with the least obstruction, 
and a symmetrical plant is usually an unobstructed one. 
Just how much sunshine is essential has not been fully determin- 
ed, so far as I can learn, but that plants differ much in their re- 
quirement, and also adapt themselves rapidly in this, as in tem- 
perature and moisture, is well known. An almost cloudless sky 
for months will not harm many plants if they have an abundance 
of moisture, and it is probable that others would be equally im- 
mune if they were gradually acclimated. Experiments in Paris 
carried on through a period of five years, in which sunshine, heat, 
rainfall, and evaporation were carefully measured from March to 
July, inclusive, showed that a considerable increase in crop yield 
was obtained when the percentage of sunshine was greatest, al- 
though at no time during the period was there a very marked dif- 
le: ence in the amount of sunshine measured. 
Other climatic elements which can be considered of value in re- 
lation to vegetation are wind direction, wind velocity, and eva- 
poration. The wind direction and velocity of all parts of the 
United States have been determined with reasonable accuracy, 
and should be available to anyone seeking this information. The 
damaging effects of high winds can be largely controlled by the 
cultivation of wind-breaks. These will quickly and permaently 
prevent drifting of the soil, too rapid evaporation by high winds, 
broken and fallen grain, due to the same cause, and, to a consider- 
