SEEDS AND SEEDLINGS. 53 



* 88. Pine. In a Pine seed notice the thin wing, serving for wind- 

 dispersal. Dissect the seed and notice the embryo (consisting of 

 radicle, hypocotyl, and numerous cotyledons in a circle around the 

 plumule) surrounded by the endosperm. Sketch the stages in ger- 

 mination (Fig. 28). 



89. The Uses of Cotyledons. From the seedlings you 

 have studied, you will observe that the cotyledons, or first- 

 formed leaves of the young plant, have different functions 

 or uses in different plants. They are always concerned with 

 the feeding of the young root and shoot, but they carry out 

 this duty in different ways. When the seed contains no 

 food stored outside of the young plant, the cotyledons 

 usually contain food. In a few plants e.g. Broad Bean 

 and Peas the cotyledons are food- stores and nothing more ; 

 they remain below the ground, simply yielding up the food to 

 the growing root and shoot, and are termed "hypogeal" 

 (= below ground). 



In most non-endospermic plants, however, the cotyledons 

 are carried up into the air and become green, and like all green 

 leaves manufacture food (Ch. IV.) ; even in these cases, where 

 the cotyledons are " epigeal " (= above ground), they contain 

 more or less food, though the amount is often scanty e.g. 

 Cress, Mustard and they have a double function, first sup- 

 plying stored food and then making fresh supplies. In seeds 

 whose food is stored outside of the embryo, the cotyledons 

 either remain within the seed and act as digesting and ab- 

 sorbing organs, as in Wheat, Maize, Date ; or they first digest 

 and absorb the food-store in the endosperm, and then emerge 

 from the seed and become the first green leaves of the plant 

 (Castor Oil, Ash, Onion, Pine). 



90. Types of Germination. From the foregoing, it is 

 easy to see that the various seedlings we have studied fall 

 under one or other of four main types, distinguished by 

 presence or absence of endosperm in the seed and by the 

 behaviour of the cotyledons in germination. As we have 

 seen, the chief functions of cotyledons are (1) to store food, 

 (2) to digest and absorb food stored in the endosperm, (3) to 

 manufacture food. The cotyledons may perform only the 

 first or only the second of these three functions, or they 

 may proceed to carry on the third function after they have 



