STRUCTURE OF THE SEED. 209 



On one part of the surface of the episperm we see constantly 

 the hilum, a scar marking, the point by which the seed was 

 attached to the funiculus or placenta whilst in the pericarp 

 (Fig. 103.) a. The hilum is more or less conspicuous on the epis- 



Fig. 103. 



Fig. 103. Leguminous seect. a. The tilum under the form of a linear cicatrice. &. 

 The micropyle. 



perm of all seeds, its color being very frequently quite different 

 from the color of the rest of the surface of the seed. The 

 hilum is very conspicuous' in the bean and pea, being quite 

 black in the former. It is by the hilum that the nourishing 

 vessels of the pericarp penetrate the seed. They traverse the 

 double or single membrane of the episperm, and enter the 

 nucleus or kernel by the chalaza, a term applied to the fibro- 

 vascular bottom of the nucleus or kernel where it unites with 

 the episperm. 



On the surface of the episperm, we perceive frequently very 

 near to the hilum or in a point diametrically opposite to it a 

 punctiform opening extremely small which is called the micro- 

 pyle. (Fig. 103.) 6. The micropyle is simply the foramen or open- 

 ing of the two membranes of the ovule which is contracted to a 

 point, so as to become sometimes hardly perceptible. The 

 micropyle may be readily detected in the pea or bean in the 

 form of a small hole or point which in this instance is near the 

 hilum. The micropyle always corresponds to that point of the 

 nucleus where the embryo sac is formed, and the summit of 

 which gives birth to the embryonic vesicle. It follows from 



