lii INTRODUCTION TO BOTANY. 



Observe, when the tropJiosperm or podosperm covers the 

 seed so as to embrace it to a greater or less extent, this pro- 

 longation takes the name o^arillus. 



We will next examine 



The Seed. 



Every seed, essentially contains an organized body, which, 

 becoming developed, produces a being, perfectly similar to 

 that which gave it birth : this body is the embryo^ the essence 

 of the seed. The seed is composed of two parts ; 1st. the 

 episperm^ or proper covering : 2nd. the Jcernel within the epis- 

 perm. The point of the seed by which it is connected with 

 the pericarp, is called umbilicus, or hilum : this last, is always 

 marked with a kind of scar. The centre of the hilum always 

 represents the base of the seed. The summit of the seed is 

 the point opposite to the hilum. 



For a minute account of the several parts above named, and 

 much additional matter, the reader is referred to Richard's 

 Introduction, and to Lindley's. 



Germination of Seeds. 



Seeds through time, lose their germinative power. Some 

 retain this power for a considerable number of years ; for 

 example, kidney-beans, kept for sixty years, have germinated. 

 Seeds of the sensitive plant have been perfectly developed 

 about one hundred years after they have been gathered. In 

 these cases, they must have been excluded from the air, 

 light, and moisture. 



Water, heat, and air are necessary agents for germination. 



Seeds, plants, and animals can neither grow, respire, nor 

 live in pure oxygen gas : the best mixture for the purposes 

 above, is in the proportion of one part of oxygen, and three 

 parts of azote, (that is, nitrogen,) or of hydrogen. 



From the moment the embryo of a seed becomes developed, 

 it takes the name o^ pla^ihde. Its two extremities grow in 

 opposite directions. The one is formed by the gemmide, and 

 grows upwards into the air ; this is called the caudex ascendens. 



