TRANSFORMATIONS OF LEAVES 55 



that the two or three upper leaflets are transformed into 

 tendrils for climbing. In 

 the sweet pea all but the 

 two lowest leaflets have 

 been developed into ten- 

 drils. 



68. Scale Leaves. 



Sometimes the leaf disap- 

 pears entirely, or is reduced 

 to a mere scale or spine, 

 as in the cedar and most 

 cactuses, and some other 

 part takes its place, but it 

 can always be recognized 

 by its position on the stem, 

 just below the point where 

 a bud appears. Ordinarily, 



buds never OCCUr anywhere i6.- Leaf of common pea, showing upper 

 * leaflets reduced to tendrils. 



except at the axil, and this 



position is so constant that it will generally serve to dis- 

 tinguish leaves from other organs under all disguises. 

 In the common asparagus, the green threadlike appendages 

 which are usually regarded as foliage, spring each from 

 the axil of a little scale. This, as has just been stated, 

 is the normal position of a bud or branch, and hence, 

 botanists conclude that here a double transformation has 

 taken place, of leaves into scales and branches into foliage. 

 Scale leaves are of use to plants that have need to pro- 

 tect themselves against frost and snow, like the heaths and 

 mosses of cold regions. They are common also in hot and 

 arid districts where it is necessary to reduce the surface 

 exposed for transpiration, though here they are more apt 

 to take the form of prickles and spines as a double protec- 

 tion against sun and animals. 



69. Leaves as Storehouses of Food and Moisture. Of 

 this we have familiar examples in the cabbage and other 



