We can demonstrate the fact, however, in the case of man by the help of certain very interesting measurements which have been recorded by Daffner[148], of the height of German cadets, measured at half-yearly intervals. _Growth in height of German military Cadets, in half-yearly periods._ (_Daffner._) Height in cent. Increment in cm. Number ─────────────────────── Winter Summer observed Age October April October ½-year ½-year Year 12 11–12 139·4 141·0 143·3 1·6 2·3 3·9 80 12–13 143·0 144·5 147·4 1·5 2·9 4·4 146 13–14 147·5 149·5 152·5 2·0 3·0 5·0 162 14–15 152·2 155·0 158·5 2·5 3·5 6·0 162 15–16 158·5 160·8 163·8 2·3 3·0 5·3 150 16–17 163·5 165·4 167·7 1·9 2·3 4·2 82 17–18 167·7 168·9 170·4 1·2 1·5 2·7 22 18–19 169·8 170·6 171·5 0·8 0·9 1·7 6 19–20 170·7 171·1 171·5 0·4 0·4 0·8 In the accompanying diagram (Fig. 30) the half-yearly increments are set forth, from the above table, and it will be seen that they form two even and entirely separate series. The curve joining up each series of points is an acceleration-curve; and the comparison of the two curves gives a clear view of the relative rates of growth during winter and summer, and the fluctuation which these velocities undergo during the years in question. The dotted line represents, approximately, the acceleration-curve in its continuous fluctuation of alternate seasonal decrease and increase. ―――――――――― In the case of trees, the seasonal fluctuations of growth[149] admit {119} of easy determination, and it is a point of considerable interest to compare the phenomenon in evergreen and in deciduous trees. I happen to have no measurements at hand with which to make this comparison in the case of our native trees, but from a paper by Mr Charles E. Hall[150] I have compiled certain mean values for growth in the climate of Uruguay. [Illustration: Fig. 30. Half-yearly increments of growth, in cadets of various ages. (From Daffner’s data.)] _Mean monthly increase in Girth of Evergreen and Deciduous Trees, at San Jorge, Uruguay._ (_After C. E. Hall._) _Values expressed as percentages of total annual increase._ Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Evergreens 9·1 8·8 8·6 8·9 7·7 5·4 4·3 6·0 9·1 11·1 10·8 10·2 Deciduous trees 20·3 14·6 9·0 2·3 0·8 0·3 0·7 1·3 3·5 9·9 16·7 21·0