INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH 



2 °5 



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 

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

 116). 



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



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. Ra>i- 

 unculns 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 

 (Fig. 117, 2). Several kinds of leaves are frequently found on the same stem. 



