LEAVES 



35 



light, but they produce leaves reduced in size and without 

 green tissue. Often these scales seem to be merely useless 

 relics (Fig. 64); but sometimes they are used for food 

 storage, as in lily bulbs, onions, etc., which are mostly made 

 up of fleshy scales (Fig. 65). 



In the scaly buds, so common on shrubs and trees, the 

 overlapping scales are clearly protective structures, and to 

 this end are generally firm and resistant, often coated with 

 resin, the inner ones being frequently clothed with woolly 

 hairs. 



(2) Tendrils. The whole leaf or some of its branches 

 may develop as tendrils, the latter case being illustrated by 

 the sweet pea (Fig. 32). Ten- 

 drils are sensitive to contact 



and aid in climbing. Some- 

 times leaves act as tendrils 

 without any modification of the 

 blade, the petiole being sensitive 

 to contact and encircling sup- 

 ports like a tendril, as in the 

 garden nasturtium. 



(3) Thorns. Leaves develop- 

 ing as thorns may be observed 

 in the barberry (Fig. 33). In the 

 common locust, acacia, etc., only 

 the stipules develop as thorns. 



Both tendrils and thorns are 

 also developed as stem struc- 

 tures, being modified branches. 



(4) Leaves of pitcher-plants. 

 In these plants the leaves form 

 tubes or urns of various forms, 

 which contain water; and to these 



insects are attracted and drowned. The common pitcher- 

 plant of the northern States, a Sarracenia, is a well-known 



FIG. 32. Pinnately compound 

 leaf of garden pea, whose ter- 

 minal portion has developed 

 as tendrils. After STRAS- 



BURGEK. 



