PART I. MORPHOLOGY. 



12 



rf) ; in Lathyrus Aphaca all the leaflets undergo this metamor- 

 phosis, and the special functions of the foliage-leaves are discharged 

 by the stipules. The tendrils of the Cucurbitacese are also metamor- 

 phosed leaves. 



3. Leaf-Spines are leaves or parts of leaves which are modified 

 into pointed, hard, woody structures. Spiny teeth are often present 

 on foliage-leaves (e.g. Holly, Thistles) ; in species of Caragana and 

 Astragalus the phyllopodium of the pinnate leaf becomes a spine 

 after the falling-ofF of the green leaflets ; finally, the entire leaf 

 becomes spiny in Berberis (Fig. 29). 



4. Scales or cataphyllary leaves (Fig. 27 N). These are usually 



of a yellow or brown colour, of simple 

 structure, without projecting veins, and 

 are attached to the stem by a broad 

 base. They may be regarded in some 

 case as leaf-bases, the laminse of which 

 have not developed ; and in other cases, 

 as entire leaves which have remained 

 in a rudimentary condition. They al- 

 ways occur on subterranean stems (e.g. 

 the scales of the Onion, see also Figs. 

 13 and 14 n\ and sometimes on aerial 

 stems. Many plants which are not 

 green (Orobanche, Neottia) produce only 

 cataphyllary leaves in addition to the 

 floral leaves. The most common form 

 in which they occur upon aerial stems 

 is that of scales investing the buds of 

 trees. In this case they are the lowest 

 leaf-structures borne by the annual 

 shoot, and usually fall off as the bud 

 developes. 

 Some few indigenous trees have naked buds without scales, as 



Viburnum Lantana, Cornus sanguinea, Rhamnus Frangula; 



their buds are protected by a dense growth of hairs. 

 The following varities of bud-scales may be distinguished : 

 a. The bud-scales are the stipules of leaves which develop a lamina ; as 



m Alnus, Liriodendron, Marattiacese. 

 6. The bud-scales are the stipules of leaves which develop no lamina : 



Oak, Beech. 



c. The bud-scales are leaf-bases, the lamina not being developed ; Maple, 

 Ash, Horse-Chestnut, Prunus Padus. 



FIG. 29. Leaf-spines of Berberif 

 tulgaru, at the base of a shoot of 

 one year's growth : a leaf-spine 

 with broad surface; b with a 

 smaller surface ; fc fc axillary buds 

 (nat. size). 



