240 



PLANT STKUCTUKES 



leaf) and Alisma (water-plantain), in which there is a dis- 

 tinct calyx and corolla. The genus Tiji)lia (cat-tail) is also 

 an aquatic or marsh form of very simple type, the flow- 

 ers being in dense 

 cylindrical clusters 

 {sjnhes), the upper 

 flowers consisting of 

 stamens, the lower of 

 carpels, thus forming 

 two very distinct re- 

 gions of the spike 

 (Fig. 221). 



132. Grasses. — 

 This is one of the 

 largest and probably 

 one of the most use- 

 ful groups of plants, 

 as well as one of the 

 most peculiar. It is 

 world-wide in its dis- 

 tribution, and is re- 

 markable in its dis- 

 play of individuals, 

 often growing so 

 densely over large 

 areas as to form a 

 close turf. If the 

 grass -like sedges be 

 associated with them 

 there are about six 

 thousand species, 

 representing nearly 

 one third of the Mon- 

 ocotyledons. Here 

 belong the various 

 cereals, sugar canes. 



Fig. 222. A common meadow grass (Festuca) : A, 

 portion of flower cluster (spikelet), showing the 

 bracts, in the axils of two of which flowers are 

 exposed ; B, a single flower with its envelop- 

 ing bract, showing three stamens, and a pistil 

 whose ovary bears two style branches with much 

 branched stigmas.— After Strasburger. 



