20 BOTANY 



condition, clothed with a separable protective coat, and 

 supplied with a certain quantity of food stored in it or 

 around it by the parent from which it came. In its 

 quiescent condition this young plant is called an embryo. 

 It consists of a young root and a young shoot, the latter 

 being composed of a stem on which are borne a certain 

 number of leaves. These parts are known as the 

 radicle and plumule respectively, the first-formed leaves 

 being called cotyledons. The number of cotyledons 

 varies ; in most cases there are two, in others one, while 

 in others again there may be several. The number of 

 cotyledons is constant throughout large groups of plants 

 and is associated with differences of structure of the 

 other parts of the plant. The first two groups referred 

 to are called Dicotyledons and Monocotyledons. In 

 another group called the Gymnosperms we find a 

 variable number, sometimes as many as fifteen. 



The young embryo is fitted to bear separation from 

 the parent and transport to different situations by the 

 fact that its life is in a dormant state and that it is 

 protected by the skin or testa of the seed. Under 

 appropriate conditions it can resume active life and 

 grow into an adult plant, provision having been made 

 for its nutrition during the early stages of its develop- 

 ment and until it acquires the power of making its own 

 food. This necessary food is prepared by the parent 

 plant and is originally deposited as a relatively bulky 

 mass around the embryo in its early development in a 

 particular cell known as the embryo sac. This food con- 

 stitutes what is known as the endosperm, a collection 

 of cells which fill up all the space in the embryo sac 

 which is not occupied by the embryo. 



The cells of the endosperm with their contents are all 

 provided for the nourishment of the embryo. In some 

 cases the embryo feeds upon this store while very 

 immature and before it assumes its quiescent state. In 



