PART I 



THE STRUCTURE AND PHYSIOLOGY OF 



SEED PLANTS 



CHAPTER I 

 THE SEED AND ITS GERMINATION 



The seed. A seed is a miniature plant, 

 or embryo, with some accessory parts, in a 

 resting or dormant state, and capable under 

 suitable conditions of reproducing the kind 

 of plant which bore it. 



The power of producing seeds is peculiar 

 to the higher plants (seed plants, or sper- 

 matophytes) and sharply distinguishes them 

 from all lower forms of plant life. 



The embryo may nearly or quite fill the 

 interior of the seed, as in Fig. 1, or it may 

 constitute only a small part of the bulk of 

 the latter, as in Figs. 3, 4. 



2. Form and position of the embryo. 



mi i i v , r? FIG. 1. Lengthwise sec- 



llie embryo shows great diversity ot form ; . 



tion of a squash seed 



it may have one, two, or several seed leaves, 



c, hypocotyl ; co, cotyle- 



or cotyledons (Figs. 1, 3, 12). These may don; e, endosperm ; A, 

 be straight, as in the squash seed, or much hllum: p plun ^. le j 



t, testa. Magnified 



curved and folded, as in the seed of the about two and a half 

 four-o'clock, morning-glory, or buckwheat, 

 but they are almost always closely packed for economy of space. 



5 



-c 



