SECT. I MORPHOLOGY 31 



metamorphosed shoots, exhibit a limited apical growth like that of 

 ordinary leaves. 



We have already seen that in certain cases the apical cone may give rise to a 

 terminal leaf. The apex of the leaf in many ferns (e.g. Adiantum Edgeworthii) may 

 on the other hand be transformed into a bud from which a shoot will develop ( 13 ). 



The unsegmented protuberance of the still rudimentary leaf, termed 

 by EICHLER ( u ) the primordial leaf (Fig. 32 A ft), first projects from 

 the vegetative cone of the 

 shoot (A v). This is usually 

 followed by a separation of 

 the primordial leaf into the 

 LEAF-BASE (g in A and B) 

 and the rudimentary lamina 

 or UPPER LEAF (o in A and 

 B). The leaf-base, or the 

 part of the rudimentary leaf 

 which immediately adjoins 

 the vegetative cone, either Fl0 ' 3 "- A i )ex of au Klm shoot - Vl "< j>erfri. A, 



. ' . , . , Showing the vegetative cone r, with the rudiment! 



takes I1O further part in the of a young leaf, 6, still unsegmented, and of the next 



Succeeding differentiation of older leaf, exhibiting segmentation into the laminar 



thp Ipnf or ir dpvplnns intn rudiment, o, and leaf-base, g; , showing the older 



uie leai, o leveiops into ]|laf viewed obliquely frolll behilld> (x 58 } 

 a LEAF -SHEATH (vagina) or 



into STIPULES. The upper leaf, on the other hand, gives rise to the 

 leaf-blade or LAMINA. If the fully developed leaf possesses a LEAF- 

 STALK (petiole), this is later interposed by intercalary growth 

 between the leaf-blade and the leaf-base. 



The leaf-tip often develops more rapidly than the rest of the leaf, and GOEBEI. 

 regards this as an arrangement for the protection of the younger parts of the 

 bud ( ls ). This is seen most strikingly in some tropical plants, especially in climbers. 

 In this case, according to M. RACIBOKSKI ( I8 ), the "fore-runner tips" serve for 

 assimilation before the remainder of the leaf has attained the mature condition. 



In leaves the laminae of which do not remain simple, but undergo segmenta- 

 tion as they develop, the lateral segments are as a rule formed in the basipetal 

 direction, i.e. from the tip towards the base (Fig. 33) ; the opposite direction of de- 

 velopment is, however, sometimes found. The segments of the palmate and pinnate 

 leaves of Palms originate by a process of splitting of the leaf blade which is, to begin 

 with, entire. The direction of the splits is determined by the folds of the lamina ( 17 ). 



Different forms of leaves are most clearly seen in the Phanerogams, 

 in which the various leaf structures found at different regions of the 

 shoot have been distinguished as SCALE LEAVES, FOLIAGE LEAVES, 

 BRACTEAL LEAVES, and FLORAL LEAVES (Fig. 34). These usually 

 succeed one another in definite order. However unlike the leaves 

 may become, their first origin -is similar. Since the scale leaves and 

 bracts can often be shown to be arrested forms of foliage leaves, the 

 latter may be first considered. 



