DIV. I 



MORPHOLOGY 



107 



leaves forming a whorl may arise in the same way and only later 

 appear as distinct structures on the ring-shaped outgrowth. When 

 whorled leaves arise independently they may either appear simul- 

 taneously or, as is more 

 commonly the case, in suc- 

 cession ( 58 > 59 ). 



In rare cases a leaf may be 

 terminal on the growing point. 



While the shoot bymeans 

 of its growing point has an 

 unlimited growth, the growth 

 of the leaf primordia, which 

 only continues at their tips 

 for a short time, is limited. 

 The tip, which often develops 

 more rapidly than the rest of 



FIG. 123. Lily of the Valley (ConvaUaria mnjalis). nd, 

 Scale leaves ; Ib, foliage leaves ; hh, bracts ; b, flower ; 

 u-s, rhizome; aw, adventitious roots. (Somewhat 

 reduced. After STRASPURGER.) 



G. 1 -24. Bird Cherry (Prunus 

 arium). Bud-scales (1-3) and the 

 transition forms (4-6) to the foliage 

 leaf (7) ; sp, leaf-blade ; , leaf-stalk; 

 nb, stipules. (Reduced slightly. 

 After SCHENCK.) 



the leaf, is first transformed into permanent tissue. This assists in 

 the protection of the youngest parts of the bud, a function which has 

 already been seen to be undertaken by the leaves. The further growth 

 of the leaf is as a rule effected by intercalary growth. Most frequently 

 the change into permanent tissue proceeds from the tip towards the 

 base. The growth is thus greatest and most prolonged in the leaf- 

 base, where it continues until the leaf is fully developed. 



