32 BRITISH FLOWERING PLANTS chap. 



snugly the bud nestles between the stump of the 

 terminal shoot and the petiole of the leaf. The same 

 thing occurs in the Elm, Birch, Hazel, Lilac, Willow, and 

 others. In these and many other species the bud situated 

 apparently at the end of the branchlets is in reality 

 axillary, as is shown by the presence of a terminal scar, 



due to the fall of the true ter- 

 minal bud. I have found that 

 even at the end of May the ter- 

 minal buds of the Lime have 

 almost all died and fallen aM'ay. 



But why do the terminal buds 

 wither away ? In some cases the 

 bud contains a definite number 

 of leaves, but in the genera above 

 mentioned the number is inde- 



Fia. 16. — Young shoot of Horn- r. ■, , i , 



team, x 2. j}, base of hnite — morc than can come to 

 petiole, tiie upper part having maturity ; and vct the rudiments, 



been cut off ; b, bud ; t, ter- i • i _l j. i j. i 



niinai shoot, the upper part which are constructed to procluce 

 of which has ah-eady dropped ^^^^ leaves, cauuot modify them- 



ont ; s, scar of stipule. . ' , "L , 



selves into bud scales, ihus m 

 the Ash, Maple, Horse-chestnut, and Oak, which have 

 true terminal buds, there are comparatively few leaves ; 

 while in the Elm there are about seven ; Hornbeam, 

 eight ; Lime, eight ; Willow, fifteen ; and Lilac, fifteen. 

 In the above species it is generally the uppermost lateral 

 bud or buds which develop, but in some cases, as in 

 Viburnum Opulus (Guelder Rose), Gymnocladus, and 

 others, these also perish, and as a rule only the lower 

 ones grow, and the upper part of the stem dies back. 



The fall of the leaf in autumn is by no means a simple 

 process, or a mere case of death. In the first place, the 

 chlorophyll substance is too valuable to be lost and 

 thrown away. Sachs has satisfied himself that it 

 passes out of the leaf, down the petiole, and thus 

 migrates into the persistent parts of the plant, and is 

 stored up for future use. With the general disappear- 

 ance of the cell contents, the protoplasm and cell 

 nuclei are dissolved, the chlorophyll corpuscles lose 



