ANGIOSPERM^E 



383 



The fruit in all of the Helobiese, except the Hydrocharitaceag, is a nutlet, or 

 a dry or fleshy drupe-like achene (Potamogeton). In Vallisneria and Elodea 

 it is a leathery, elongated pod, containing a gelatinous substance, which finally 

 bursts open the fruit, and discharges the seeds. 



The Helobiese are divided into the following families : Naiadacese, Potamogeto- 

 naceae, Lilseacese, Juncaginaceae, Apono- 

 getonaceae, Alismaceae, Hydrocharitacese. 



Order II. Pandanales 



The Pandanales comprise only a 

 few forms, which are to be con- 

 sidered as primitive types. Some 

 of them, like Typha and Spar- 

 ganium, are simple aquatic plants, 



FIG. 3.56. Sparganium eurycarpum. A, 

 part of inflorescence, with pistillate 

 flowers, Q. B, two heads of staminate 

 flowers, enlarged. C, single pistillate 

 flower, enlarged. D, fruit, enlarged. 

 E, section of the fruit (nutlet) contain- 

 ing the seed. 



while others, the Screw-pines (Pan- 

 danaceae) are among the largest 

 members of the group. 



Classification of Pandanales 



FIG. 357. Dactylis c/lomerata (X J). 

 (After BAILEY.) 



The Pandanales are divided into 

 the following families : Typhaceae, Sparganiaceae, and Pandanaceae. 



Fam. i. Typhaceae. The Typhaceae are represented by the single genus 

 Typha, the common Cat-tail. These are considered to be the simplest members 



