68 BUDS AND STIPULES 



purpurea, which naturally sink at night (the plants 

 growing out of doors), and looked at them early on 

 several successive mornings, after they had assumed 

 their diurnal positions. The difference in the amount 

 of dew on the pinned-open leaflets and on those 

 which had gone to sleep was generally conspicuous, 

 the latter being sometimes absolutely dry. whilst the 

 leaflets which had been horizontal were coated with 

 large beads of dew. This shows how much cooler the 

 leaflets fully exposed to the zenith must have become 

 than those which stood almost vertically, either upwards 

 or downwards, during the night. 



' From the several cases above given there can be no 

 doubt that the position of the leaves at night affects 

 their temperature through radiation to such a degree 

 that, when exposed to a clear sky during a frost, it is a 

 question of life and death.' 1 



It is probable, however, that in some cases, at any 

 rate, this position is assumed as a protection against 

 too intense light. 



The principal modes by which buds are protected 

 are : 



1. By the expanded base of the preceding leaf. 



2. By scales which represent modified outer leaves. 



as in Willows, Ash. 



3. By the outer leaf-stalks, as in Maples, Ash. 



4. By stipules, as in the Beech, Oak. 



1 Loc. cit. p. 293. 



