ELEMENTS OF STRUCTUKAL BOTANY. 



CHAPTER IX. 



CHARACTERISTICS POSSESSED IN COMMON BY ALL THE PLANTS 



PREVIOUSLY EXAMINED. STRUCTURE OF THE SEED 



IN DICOTYLEDONS. 



57. Before proceeding further in our examination of 

 plants, "we shall direct your attention to some characters 

 of those already examined, which they all possess in 

 common. The leaves of every one of them are net- 

 veitied. Some leaves, at least, of each of them have dis- 

 tinct petioles and blades. The parts of the flowers we 

 found, as a general thing, to be in Jives. In one or two 

 instances they were in /ours, that is, four sepals, four 

 petals, and so on. 



58. Now, in addition to these resemtlances there are 

 others which do not so immediately strike the eye, but 

 which, nevertheless, are just as constant. One of these 

 is to be found in the structure of the embryo. Take 

 a cucumber or pumpkin seed, and having soaked it 



for some time in water, remove the 

 outer coat. The body of the seed 

 will then readily split in two, except 

 where the parts are joined at one 

 end. (Figs. 67, 68, 69). The thick 

 Fig. 67. Fig. 68. Fig. 69. lol>es are called cotyledons, or seed- 

 leaves, and as there are two, the embryo is dicotyledonous. 

 The pointed end, where the cotyledons are attached, and 

 from which the root is developed; is called the radicle. 

 Between the cotyledons, at the summit of the radicle, 

 you will find a minute upward projection. This is a 

 bud, which is known as the plumule. It developes into 

 the stem. 



59. If you treat a pea or a bean (Figs". 70, 71), in the 

 same manner as the cucumber seed, you will find it to be 



