70 LABORATORY AND FIELD EXERCISES 



with a hand lens. What is the nature of the stigniatic 

 and stylar surfaces ? Are they smooth or rough ? 

 3. Remove the perianth from one side of a flower so as to 

 expose the essential organs in their natural position. 



a. Sketch the essential organs accurately and indicate in 



outline the relation of the perianth to these organs. 



b. Make an accurate drawing of the pistil, indicating the 



position of the placenta and ovules and the peculiar 

 structure of the stigma and style. What advantages 

 are there for pollination in the structural relations 

 of the style and stigma ? Label all of the above 

 figures accurately. See Fig. 89 of the text. 



CROSS-POLLINATION 



Select a flower of some member of the pea family for the 

 following experimental study of cross-pollination : 



1. Press down the keel petals with the point of a pencil or 



with a dissecting needle. Eesult ? Where would an in- 

 sect need to alight in order to imitate the above action 

 of the keel, stamens, and pistil ? If an insect should 

 visit a series of flowers like the one experimented upon, 

 would cross-pollination be secured ? Be able to explain. 



2. Read the account in the text (p. 170) on cross-pollination 



in the common locust (Robinia pseudo-acacia). 



a. Does the flower upon which you experimented possess 



the contrivances of the locust flower for securing 

 cross-pollination ? If not, in what respect does it differ 

 from the locust ? 



b. Construct a drawing to show the relation of the anthers 



to the stigma and of both anthers and stigma to the 

 keel, when the latter is depressed. Compare the figure 

 with your first figure of the flower with one half of the 

 corolla removed. 



