CH. IX] 



VERTICAL SECTION OF BUD 



65 



The second of the two actions referred to is the 

 outward thrust of the expanding 

 leaves and stem, which drives the 

 bud-scales asunder. Both of these 

 actions are referable to the same 

 cause, the absorption of water by 

 the millions of minute microscopic 

 cells of which the young leaves and 

 the tip of the axis bearing them 

 are composed, and their consequent 

 growth. We know from experi- 

 mental evidence that the pressures 

 exerted by such growing organs 

 may be enormous. 



In the diagram of a bud in 

 vertical section, shown in Fig. 44, 

 the axis bears seven pairs of ap- 

 pendages, inserted at the levels 

 left unshaded, i.e. the nodes. The 

 lowermost two pairs are true bud- 

 scales, we will assume, and the next 

 inner pair are intermediate scales ; 

 then come four pairs which will 

 be true foliage leaves, though at 

 present they are very young. 



In the diagram, Fig. 45, we 

 have a representation of the relative state of affairs when 

 the bud has " burst," and the young shoot elongated. The 

 two pairs of bud-scales at the base have been thrown 

 outwards, and will soon fall off, and we observe that they 

 have neither grown in length nor been driven further 

 apart by any essential elongation of the internode between 

 them : nor do they bear buds in their axils. The next 

 pair of organs have elongated, and developed a rudiment 



w. I. 5 



Fig. 44. Diagram of a 

 bud with opposite leaves 

 and bud-scales, in longi- 

 tudinal section. The nodes 

 are left unshaded ; the in- 

 ternodes are shaded. The 

 axis bears seven pairs of 

 scales or leaves, in various 

 stages of development, 

 covering and protecting 

 the vegetative cone at the 

 apex. See Fig. 45 for fur- 

 ther development. 



