INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH 267 



Other arrangements are exhibited by Dischidea rafflesiana, a climbing plant 

 with two kinds of leaves; some of the leaves have the usual form, but others are 

 like bags or pouches, with an opening above. A vigorous aerial root arises 

 from the stem at the place of attachment of the bag and grows down into the 

 cavity of the latter. Water collects in the bag when it rains, and this stored 



Fig. 116. — Dischidia rafflesiana, showing sack-like leaves with aerial roots in the cavity. 



water is absorbed by the root and thus transferred to the rest of the plant (Fig. 

 116). 



Aquatics are likewise distinguished by special structures. Their weak stems 

 are permeated with numerous air passages. The submerged leaves usually 

 have deeply cleft lamina, with filamentous lobes. When such plants develop 

 on land, however, the form of the leaf often becomes remarkedly altered. Ran- 

 unculus fluitans, for instance, is such an aquatic with filamentous leaves (Fig. 

 117, 1). When growing on land the aerial leaf has the typical broad lamina 



