CHAPTER XVI. THE SPERMAPHYTA. . 385 



In germination, also, the embryo behaves differently from 

 that of Monocotyledons, in the relatively strong growth which 

 the primary root or radicle always makes. It pushes out of the 

 seed-coats and attains a considerable size, even while the rest of 

 the embryo is still contained within the seed. See Fig. 578. The 

 cotyledons may either remain enclosed within the seed-coats and 

 wither, after the nutriment in them has been exhausted, or they 

 may be carried above-ground, performing for a time the functions 

 of foliage leaves. 



To the Dicotyledons belong all the trees, except the Pines and 

 their congeners, and nearly all the shrubby plants and a large 

 portion of the herbs that constitute the native flora of the north- 

 ern United States. They form by far the largest group of flower- 

 ing plants, much larger, in fact, than all the others combined. 

 About two hundred natural orders, including upwards of eighty 

 thousand species, are recognized by botanists. 



They are divided into three principal divisions, as follows : 



Division A. — The Apetalce. 



Division B. — The Gamopetalce. 



Division C. — The Choripetalce. 



(A) The Apetalae have usually small and inconspicuous 

 flowers, which are mostly destitute of a corolla, and frequently 

 also of a calyx. There are two subdivisions, the Juliflorce and 

 the Ccnirosperma. 



TheJuIiJiorcB have their small flowers usually arranged in 

 spikes, catkins, heads, or sometimes panicles ; the flowers are 

 mostly separated, the staminate and pistillate occurring in dis- 

 tinct clusters, sometimes both on the same plants, sometimes on 

 different plants. The group is represented by the Amentaceee, 

 including the Birches, Oaks, Walnuts, Hazels, Sweet-gales, Wil- 

 lows and Casuarinas ; the Piperineee, including the Peppers, 

 Lizard-tails and Chloranths, and the Urticinece, including the 

 Nettles, Elms, Hackberries, Bread-fruits, Figs, Mulberries, Syca- 

 mores and Hemps. 



The Centrospermce usually have hermaphrodite flowers, with a 

 one, or rarely two, whorled perianth, frequently twice as many 

 stamens as sepals, and superior, usually one-celled ovaries, which 

 either produce a single, basilar campylotropous ovule or a cen- 

 tral placenta, bearing numerous ovules. The group includes the 



