PLANT ORGANS AND ORGANISMS 215 



of nourishing substance, thus resulting in the formation of abundant 

 perisperm and a small reduced endosperm. 



Exalbuminous seeds are those in which the albumen is stored in the 

 embryo during the growth of the seed. Such seeds show the fleshy 

 embryo taking up all or nearly all the room within the seed coat. 

 Examples: Physostigma, Amygdala, etc. 



Albuminous seeds are those in which the nourishment is not stored 

 in the embryo until germination takes place. Such seeds show a 

 larger nourishing tissue region and a smaller embryo region. Exam- 

 ples: Nux Vomica, Myristica, Linum, etc. 



Gross Structure of a Monocotyl Seed (With fruit wall attached), 

 Indian Corn. The ripened seed of Indian Corn is surrounded by a 

 thin, tough pericarp which is firmly adherent to and inseparable from 

 the Spermoderm or seed coat. Because of this fact, while in reality 

 a fruit called a caryopsis or grain, this structure is sometimes erro- 

 neously termed a seed. 



The mature grain of most varieties of Indian Corn is flattened and 

 somewhat triangular in outline, the summit being broad and the 

 base comparatively narrow. The summit is indented and often 

 marked by a small point which represents a vestige of the style. 

 The basal or " tip" region marks the part of the grain which was in- 

 serted into the cob. Upon it maybe found papery chaff, represent- 

 ing parts of the pistillate spikelets. The groove noted on the 

 broader surface indicates the position of the embryo. 



Histology of the Indian Corn Seed (With fruit wall attached). If a 

 longitudinal section be cut through the lesser diameter of a soaked 

 grain, the following histologic characteristics will be observed: 



1. The Pericarp or ripened ovarian wall which, alike with all other 

 grains, adheres firmly to the wall of the seed forming a portion of 

 the skin of the grain. The pericarp comprises an outer epicarp of 

 elongated cells with thin cuticle, a mesocarp of thicker walled cells 

 without, becoming thinner within, and a layer of tube cells. 



2. The Spermoderm or seed coat, a single layer of delicate elon- 

 gated cells. 



3. The Perisperm, another layer directly underneath the Spermo- 

 derm, difficult to distinguish without special treatment, and repre- 

 senting the ripened nucellar tissue of the ovule. 



