108 FAMILIAR TREES 



textufe of the outer members of the series, and the 

 "viscid secretion with which they are bound together — 

 nay, the very presence of stipules at the base of the 

 young leaves — are all adaptations for the exposed 

 situation of the tree. It has, however, recently been 

 pointed out that these warm blanket-like wrappings 

 do not act in quite so simple a manner as might be 

 supposed : they are not mere blankets to keep out the 

 frost, for the delicate bud tissues may frequently be 

 found in winter with their moisture congealed to ice 

 in spite of all these wrappings, and without any 

 permanent injury to the embryonic shoot. It is 

 probably sudden freezing or thawing which proves 

 so fatally destructive to plant-tissues, expanding the 

 water they contain into ice-crystals, so that the 

 cells are ruptured and torn asunder in the process. 

 Leathery scales, gummy excretions, and thick felts of 

 hair would seem, therefore, to be mainly effective by 

 keeping off damp and moisture from outside and by 

 moderating any changes of temperature within the 

 protected structure, whether in a downward or in 

 an upward direction. 



No part of the plant, however, suggests this careful 

 provision against cold so much as the leaves them- 

 selves. When young they are " plicate " or plaited in 

 a somewhat fan-like manner ; but, as the secondary 

 veins spring from" the midrib in a pinnate manner, 

 and not, as in the Maples; radiating palmately from 

 the apex of the leaf-stalk, this folding is not that of 

 an ordinary fan but rather of one constructed with an 

 elongated central axis. , In addition to this plication 

 the two sides of the leaf are so folded towards one 



