Miscellaneous, 397 



during the winter, altbonpjh the weather is then milder than it is 

 in several parts of Europe during the summer. Thus, at Funehal, 

 the leaves of oaks {Quercvs pedunctdata) planted in some public 

 gardens and promenades began to grow yellow at the end of October, 

 and gradually became dried uj) to the 1st of January. Some isolated 

 trees began to shoot l)y the 10th of January, and were green again 

 on the (ith of February ; but all the others remained in a state of re- 

 pose and were not generally covered with new leaves until the 20th of 

 February. In Mr. Gordon's garden, at an elevation of 1800 feet^ 

 they were a month later. .isr sriT 



The leaves of the beech became yellow at Funehal by the 9tH/i^ 

 November, at Mr. Gordon's garden by the 28th of October. The 

 leaves, or at least the greater part of them, remained in a dry state 

 upon the trees, until tiiey began to shoot in the spring, which was 

 about the ist of April. At Funehal, the terminal buds were open 

 by the 8th of April, and the lateral a httle later. 



At Glaris, the period of repose of the beech on an average is 1 94 

 days ; in Madeira, where the cold season is like the summer at Glaris, 

 it is 149 days. The difference is only 45 days. The oak in Switzer- 

 land has a period of repose nearly equal to that of the beech, whilst 

 at Madeira it is only 110 days, or 49 days less than the beech. M. 

 Heer sup[)oses that this difference may arise from the beeches of 

 Madeira having been introduced from England and the oaks from 

 Portugal, so that the latter would have previously acquired the habit 

 of losing their leaves later and vegetating sooner than in the centre of 

 Europe. 



M. Heer ought perhaps to have added, what he no doubt knows, 

 that sudden variations of temperature in the twenty-four hours, 

 especially the instantaneous diminution to 32° Fahr. or lovver, are one 

 of the great causes of the fall of the leaves in Switzerland. The 

 absence of these variations retards the phseuomenon in the west of 

 Europe, and still more in Madeira. 



In the facts stated by M. Heer, — facts of which we previously 

 had examples in the hothouse culture of tropical plants, — there is a 

 proof of that important physiological law, too often forgotten by 

 meteorologists, that the same temperature or the same sum of tem- 

 peratures, combined with the season, does not always produce the 

 same effect upon organized beings. 



Every species is as it were a machine which performs its functions 

 under the influences of external causes, modified by particular internal 

 conditions. These vary not only between one species and another, 

 between one race of a species and another, and even up to a certain 

 point between one individual and another, but also between one period 

 and another, — the same heat after the repose of vegetation for instance, 

 not producing the same effect as in other circumstances. 



In Madeira, the Platanus occidentalis, a. n&tive of the United States, 

 loses its leaves very slowly from the middle of October, or rather they 

 gradually become yellow and fall afterwards from the action of wind 

 and rain. The repose is complete in January, February, and up to 

 April, during a period of 87 days. The Liriodendron tulipifera, also 

 a native of North America, has a complete repose of 151 days. 



