7& A NEW ZEALAND NATURALIST'S CALENDAR. 



the cells of the dividing layer, causes the fibrous tissue 

 of the leaf-stalk to be torn, and thus the leaf is quietly 

 severed and thrust away from its connection, to drop 

 by its own weight. Sometimes frost on a still night 

 causes a rapid fall of leaves on account of the freezing and 

 consequent expansion of the fluid in the separating layer. 



Before the leaf falls, its colouring matter, the chlorophyll 

 which gives it its green colour, has begun to alter in 

 chemical composition, turning at the same time yellow, 

 red, or brown. We do not know what the exact change 

 is, but no doubt there is a withdrawal from the leaf of 

 soluble materials, which are either stored up elsewhere for 

 future use or are converted into new tissue. Thus, if you 

 look at the branches of deciduous trees you will find 

 that next season's buds are already well developed, those 

 on some twigs of beech in front of me are already more 

 than half an inch in length. Then all organisms must 

 have some means of getting rid of dead and waste matters. 

 Animal organisms excrete and throw off these by a variety 

 of glands, but in the vegetable kingdom organs which 

 exist for the express purpose of getting rid of waste 

 matters are either unknown or are very rare. But in the 

 case of all the higher plan Is the leaves serve as vehicles for 

 the disposal of effete matter. Before they fall normally 

 their protoplasm and starch are absorbed back into the 

 main tissues of the plant, while deleterious matters like 

 oxalic acid are stored up in the leaves along with spare 

 lime and potash. 



This separation of leaves when their work is done serves 

 more purposes than one. If they remained on they would 

 subject the plant to strains during gales and high wind at 

 a time when the new rootlets are beginning to develop, 

 and when the branches are comparatively tense with 

 formative material. Only deciduous -leaved plants with 

 extremely tough stems, like oaks, seem able to hold the 

 leaves when the latter are dead and functionless. Further, 

 by the separation quietly of the dead leaves, these fall all 

 round the parent plant instead of being blown to a distance, 

 and thus they help to enrich the surface soil. Then worms 



