180 THE NATURE AND WORK OF PLANTS 



that the first leaf that appears is simple, the blade 

 not being divided or branched. In the bean it is 

 an active green leaf, but in the pea it is a small 

 three-pointed scale or bract which is not very 

 conspicuous and may be easily overlooked. The 

 second leaf will show greatest difference from the 

 first in the bean, and the third of that plant will 

 be very nearly the form seen on the adult stems. 

 The second leaf of the pea, however, is but little 

 more developed than the first, but the third, fourth, 

 and fifth show increased development. Perhaps not 

 until the sixth or seventh leaf is reached will you 

 find the characteristic leaf of the pea. The incom- 

 plete or simple leaves of seedlings are termed em- 

 bryonic leaves, and it is a theory of the botanist 

 that they represent forms used by the species in 

 earlier stages of its history, and these leaves are 

 the leaves of its ancestors, slightly changed of 

 course. Thus many thousands or millions of years 

 ago the group of plants from which beans have 

 sprung were furnished with simple leaves like those 

 shown just above the cotyledon. Later these plants 

 began to form lobes in the lamina, and finally it 

 was branched or divided as in the modern bean. 

 There may be still other stages between these, or 



