200 THE REPRODUCTIVE ORGANS 



The Orchid illustrates great modification in a mono- 

 cotyledonous flower. The perianth is irregular (zygomor- 

 phic) ; the posterior petal of the inner whorl projects as 

 a lip or labellum, and serves as an alighting stage for insects. 

 Below, it is prolonged into a honey-secreting spur. The 

 other petals form a hood, protecting the pollen and honey. 

 The essential organs are borne on a prolonged outgrowth of 

 the axis, called the column, on the top of which are one 

 fertile and two barren stamens, and two stigmas, also the 

 rudiment of a third stigma the rostellum (r) on which 

 are developed the two sticky bodies which glue the pollinia 

 to the bee's head. The ovary (ov) is inferior, stalk-like, and 

 twisted. When ripe, the fruit contains a large number of 

 minute seeds. 



Reference to the floral diagram (Fig. 179) will help to make 

 the various relationships clear. Six stamens, in two whorls of 

 three each, ought to be present, but of the outer whorl only 

 the anterior one is present, and it is over the rostellum. 

 The other two are suppressed, and their position is 

 represented in the diagram by a cross x . Of the inner 

 whorl, the posterior stamen is suppressed, and the two 

 lateral ones are reduced to short, barren stumps called 

 staminodes. The anterior stigma is transformed into 

 the rostellum ; the two lateral ones are functional and lie 

 below the stamen, one on either side of it. As the flower 

 develops, the stalk-like inferior ovary twists through 180 , 

 and carries all the parts of the flower round, so that the 

 posterior lip comes to be anterior in the open flower. The 

 diagram (Fig. 179) represents the parts before twisting 

 occurs. 



Flowers of Grasses. The flowers of Grasses are small, 

 and the parts can be made out only by careful observation. 

 The inflorescence is usually either a compound spike or 

 a panicle ; and what appears to be a single flower is a group 

 of sessile flowers, or spikelets (Fig. 138, 1). A dissected 



