492 



STRUCTURE AND LIFE HISTORIES 



{Alisma Plantago-aquaticd) . Like the cat- tails, the water- 

 plantains are marsh herbs (Fig. 377), with flowers either 

 perfect, monoecious or dioecious; in Alisma they are per- 

 fect, with usually six stamens. The three sepals are per- 

 sistent, but the three white petals are deciduous {i.e., falling 



Fig. 376. — Cat-tail {Typha latijolia). A, longitudinal section of 

 portion of inflorescence; Sp, spadix; p.j., pistillate flowers; s.f., staminate 

 flowers. B, pistillate flower, greatly magnified; ov, ovary; sty, style; siig., 

 stigma; sc, sterile hair; P, poUen grains, in characteristic groups of four 

 each. (Cf. Fig. 375.) 



away early). The numerous ovaries are borne in a circle 

 on a flattened receptacle. The possession of calyx and 

 corolla, together with other features, mark the family as 

 more highly organized than the cat-tails. 



429. Grass Family (Gramineae). — The grasses consti- 

 tute one of the largest, one of the most important econom- 

 ically, and one of the most difficult taxonomically, of all 



