376 THE BIOLOGY OF THE PLANT 



the structure of a pollen grain ? Does a pollen 

 grain in any way resemble a fern spore ? Draw 

 several pollen grains. Examine sections through 

 a young and through a mature anther. Does it 

 resemble a sporangium? Is it at all leaf-Hke in 

 structure ? Study cross and longitudinal sections 

 of the various parts of the pistil. ISTote particu- 

 larly the structure of the ovary, the number and 

 position of the ovules, the ridge or placenta, to 

 which each of the latter is attached by the stalk 

 or funiculus. In favorable longitudinal sections 

 through an ovule try to find the central portion, 

 the nucellus, surrounded by two coats, the inner 

 or primine and the outer or secundine'. Be- 

 tween the edges of the former look for an open- 

 ing, the micropyle, and near the centre of the 

 nucellus a large cell, the embryo-sac. In which 

 direction does the micropyle point ? Draw. "Which 

 of these parts are apparent in the mature seed? Is 

 the pistil in any respect leaf -like ? 



Study very young flower buds, and endeavor to 

 trace the origin and development of the various 

 floral organs. 



PHYSIOLOGY 



a. Fertilization. 



With a lens examine the pistils of various flow- 

 ers, as lily, pumpkin. Gloxinia, etc., for pollen 

 grains which have become attached to the stig- 

 ma. Having found such a pistil, remove it and 

 make longitudinal sections. Some of these will 

 probably show growing down into the tissues of 

 the style the tube emitted by the pollen grains. 

 Trace the tubes as far as possible and make the 



