APRIL. /5 



Chapter VI. April. 



\ UTUMX brings with it the fall of the leaf in deciduous 

 -E*- trees, and by the end of April many of the introduced 

 and a few of the native species will be bare or nearly so. 

 Oaks and some beech trees may carry their dead leaves into 

 spring, but most of them will be on the ground by the 

 beginning of winter. Reference has already been made to 

 the relation which exists between deciduous leaves and 

 snowfall, and to the changes which have led evergreen 

 forms like Fuchsias and ribbonwoods to become more or 

 less deciduous in the southern and the mountainous parts 

 of New Zealand. 



The fall of the leaf is a phenomenon so common and 

 so familiar that we seldom stop to investigate it, and 

 yet it is full of interest and instruction. I have before me 

 as I write a number of branchlets of various trees and 

 shrubs ; on some the leaves are turning yellow and a 

 few have already fallen ; others are evergreen. There 

 is nothing in an external view to suggest any difference, 

 nor is it possible to detect any by means of a hand-lens, 

 even if a section is taken longitudinally through the 

 base of a leaf-stalk. But if such a section be made thin 

 enough, and be treated with a little iodine solution, it 

 frequently reveals under the microscope the mechanism by 

 which the leaf falls. A thin plate of cells is formed right 

 across the base of the leaf-stalk, and it is at this plate that 

 the severance takes place. This plate begins to develop 

 in summer, and as the season advances one layer of 

 the cells breaks down into a thin mucilage, while others 

 lower down have their walls converted into cork. It is at 

 the mucilage layer that the dead leaf separates, while the 

 cork cells, being impervious to air and moisture, form 

 a protective covering for the exposed surface. Internal 

 pressure, caused apparently by absorption of water into 



