FOURTH EXPEDITION TO NICARAGUA Frank C. Seymour To observe the seasonal changes was the special purpose of our fourth botanical expedition to Nicaragua. Our first botanizing there hav-ing been in the winter of 1968-69; our second also in the winter of 1969-70; and our third in the spring of 1971, we made our fourth in summer, from June 27 to August 15, 1972. In a land of perpetual summer, — at least of warm weather, --how could plants know the right time to bloom? In a country where there are 365 growing days each year, what could regulate the time for harvest? One of the regulators appears to be the amount of precipitation. July and August are in the rainy season. Actually in those months in 197 2, the country was undergoing a severe drought. Excellent as this was for drying specimens in rain-forests, it was not so good for those who count-ed on a deluge of rain to grow crops. Nevertheless, enough rain fell in spring and summer so that the first feature to impress us descend-ing from the sky on the airport in Managua was the bright greenness of the vegetation in contrast to the sear brownness of the landscape in Dec-ember and January on former trips. The second factor regulating the flowering and fruiting seasons for plants could be temperature. Nicaraguans had told us that July and Aug-ust were lower in temperature than January and December. How could this amazing statement be true? In December and January, the sun, although farther away, blazed down all day long almost without interrup-tion, from a cloudless sky. In July and August, in contrast, the sun al-though nearer in the heavens, was frequently intercepted by clouds. When clouds covered the sun, it was noticeably not so hot. When there were no clouds, the heat was more intense than ever in summer. Although humans might not be aware of any coolness, the subtile difference may affect plants. Certain species with which we had become familiar in December and January were in July and August conspicuous for their ab-sence. Among many such absentees are Hyparrhenia rufa (Nees) Stapf and Tithonia rotundifolia (Miller) Blake. Another feature, astonishing to northerners, was the sight of shad-ows pointing southward! This threw me into confusion when I tried to determine compass directions in the ordinary manner of a northerner. It just didn 't work. What was wrong? Pondering to figure out the rea-son, in the course of time, I realized that the sun was nearly over the Tropic of Cancer (23 1/2 degrees N.) whereas we were south of that Tropic. We had never before been farther south than the sun. Under the circumstances, of course the shadows pointed southward. 86
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