EXPLANATION OF FIGURES IN 

 PLATES I TO XXIV. 



All figures were drawn with the aid of the Abbe* camera lucida. In some cases 

 a Zeiss microscope was used and in others a Bausch and Lomb. Various com- 

 binations of lenses were used with both instruments. The figures were reduced 

 one eighth in reproduction. The number accompanying the description of each 

 figure indicates the degree of magnification after the reduction. 



Throughout the plates the lettering is to be interpreted as follows : prothal- 

 lium (pr.), first prothallial cell (_pr.i), second prothallial cell (/r.2), third 

 prothallial or antheridial cell (a.c.), tube-nucleus (/..), stalk-cell (st.c.), stalk- 

 nucleus ($/.#.), generative cell (g*c. ), sperm-cell (s.c.), sperm-nucleus ($.#.)> 

 sperm-cytoplasm (s.cy.), spongy tissue (s./.), starch-grains (s-g"-), archegonium 

 (arch.), ventral canal-cell (v.c.), neck-cells (.c.), egg-nucleus (e.n.), cytoplasm 

 from the pollen-tube (c.p.t.), nutritive spheres (.s.), primary nucleolus (fiy.ns.), 

 secondary nucleolus (sy.ns.), receptive vacuole (r. v.~). 



All the figures have been given their normal position, as nearly as it was 

 possible to do so, on the plates. That is, they are so placed that the primary 

 axis of the ovule would be parallel with the longer axis of the plates ; and the 

 portion of a figure nearest to the micropylar end of the ovule is always towards 

 the top of the plate. 



( 154 ) 



