338 PLANT-LIFE 



cork cells appears at the point from which the withered 

 leaf of a deciduous tree falls, so as to allow no point 

 of weakness whereat fungi and bacteria could penetrate. 

 The fall of the leaf is an interesting phenomenon. The 

 leaf has done its chemistry and served its many uses; 

 the products of its labours are withdrawn into the 

 branch, and, before the leaf is allowed to fall, the layer 

 of cork cells is formed. When it has satisfactorily 

 bottled up the withdrawn products and established a 

 sufficient protection for a tender spot against invisible 

 foes, the plant permits the severance of the leaf, and 

 the protective layer of cork is seen as a " leaf-scar." 

 The scent of plants is due to the ethereal oils they pro- 

 duce. While these oils serve to attract pollinating in- 

 sects, many, if not all of them, are fatal to bacteria. 



The so-called " sleep " of flowers and leaves is a 

 provision against cold and rain. The huddling to^ 

 gether of the florets of Daisies and Dandelions is a 

 means of heat retention and also a protection of the 

 tender essential organs, as well as the pollen, against 

 the incursions of rain. We notice how on cold days 

 and during the night these flowers take up their " sleep " 

 attitude; also how they are closed on dull wet days. 

 The flowers of the Crocus are erect, and if the yellow 

 perianth leaves did not form a canopy over the tender 

 stamens and pistil on a wet day they might be seriously 

 damaged by hail or rain. "The flowers of the Crocus are 

 open only during periods of sunshine, when the essen- 

 tial organs can sustain no damage from rain, and when 

 the pollinating insects are abroad. One might instance 

 many devices for the protection of pollen. The flowers 

 of the Snowdrop and Harebell are pendulous, and their 



