204 PLANT-LIFE 



of author and space, preclude the possibility of anything 

 like a full account of these last arrivals in the plant 

 realm, nor do we find it practicable to present the reader 

 with a general survey, even were such desirable. We 

 must content ourselves with a statement of fundamental 

 characters, and an indication of the scale of forms that 

 may be regarded as lower, higher, and highest. This in 

 itself is no easy task, for the Dicotyledons are a 

 mighty assemblage, a natural unit embracing every 

 imaginable, and perhaps unimaginable, variation. In 

 the presence of such a multitude it is difficult to " see 

 wood for trees." The difficulty is accentuated by the 

 fact that it is not easy to determine whether certain 

 characters are really primitive or the results of adaptive 

 simplification. 



Dicotyledons are plants with two seed-leaves. This 

 is the most constant character throughout the class, but 

 it should be noted that there are a few exceptions in 

 which only a single cotyledon is present. This phen- 

 omenon, however, seems to be usually due to the sup- 

 pression or abortion of the second cotyledon. We may, 

 perhaps, yet discover some plants which display both 

 monocotyledonous and dicotyledonous characters, and 

 so may be certainly regarded as links between the two 

 great classes. Such would be distinctly interesting, as 

 their relations, according to present knowledge, are 

 decidedly vague. 



The typical flower of the Dicotyledons has its parts 

 arranged in whorls of four or five. In the seed the two 

 cotyledons enclose the embryo (the plumule), and on 

 germination the plumule sends a root, known in its early 

 stages as a radicle, down into the soil, and a stem into 



